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 $56.81   8.323%   $61.5383   $61.54   $61.55   $61.50  
  Purchase #2 $222.81   12.309%   $250.2357   $250.24   $250.25   $250.20  
  Purchase #3 $172.74   4.237%   $180.059   $180.06   $180.05   $180.10  
  Purchase #4 $24.74   11.454%   $27.5737   $27.57   $27.55   $27.60  
  Purchase #5 $83.44   11.278%   $92.8504   $92.85   $92.85   $92.90  
  Purchase #6 $9.83   5.607%   $10.3812   $10.38   $10.40   $10.40  
  Purchase #7 $65.62   3.488%   $67.9088   $67.91   $67.90   $67.90  
  7 purchase totals = $635.99       $690.5471   $690.55   $690.55   $690.60