Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.54   10.716%   $207.6368   $207.64   $207.65   $207.60  
  Purchase #2 $241.69   10.298%   $266.5792   $266.58   $266.60   $266.60  
  Purchase #3 $159.64   11.448%   $177.9156   $177.92   $177.90   $177.90  
  Purchase #4 $179.38   10.390%   $198.0176   $198.02   $198.00   $198.00  
  Purchase #5 $153.73   7.664%   $165.5119   $165.51   $165.50   $165.50  
  Purchase #6 $165.41   6.190%   $175.6489   $175.65   $175.65   $175.60  
  Purchase #7 $188.29   11.785%   $210.48   $210.48   $210.50   $210.50  
  7 purchase totals = $1,275.68       $1,401.7900   $1,401.80   $1,401.80   $1,401.70