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 $45.83   4.783%   $48.022   $48.02   $48.00   $48.00  
  Purchase #2 $74.49   5.553%   $78.6264   $78.63   $78.65   $78.60  
  Purchase #3 $115.75   4.217%   $120.6312   $120.63   $120.65   $120.60  
  Purchase #4 $165.50   13.300%   $187.5115   $187.51   $187.50   $187.50  
  Purchase #5 $94.74   8.554%   $102.8441   $102.84   $102.85   $102.80  
  Purchase #6 $171.85   12.759%   $193.7763   $193.78   $193.80   $193.80  
  Purchase #7 $225.73   8.668%   $245.2963   $245.30   $245.30   $245.30  
  7 purchase totals = $893.89       $976.7078   $976.71   $976.75   $976.60