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 $9.44   12.117%   $10.5838   $10.58   $10.60   $10.60  
  Purchase #2 $83.97   11.854%   $93.9238   $93.92   $93.90   $93.90  
  Purchase #3 $92.58   3.649%   $95.9582   $95.96   $95.95   $96.00  
  Purchase #4 $125.39   3.351%   $129.5918   $129.59   $129.60   $129.60  
  Purchase #5 $93.73   9.208%   $102.3607   $102.36   $102.35   $102.40  
  Purchase #6 $169.48   3.728%   $175.7982   $175.80   $175.80   $175.80  
  Purchase #7 $139.62   11.760%   $156.0393   $156.04   $156.05   $156.00  
  7 purchase totals = $714.21       $764.2558   $764.25   $764.25   $764.30