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 $84.69   9.702%   $92.9066   $92.91   $92.90   $92.90  
  Purchase #2 $247.72   9.546%   $271.3674   $271.37   $271.35   $271.40  
  Purchase #3 $15.95   4.873%   $16.7272   $16.73   $16.75   $16.70  
  Purchase #4 $114.76   5.822%   $121.4413   $121.44   $121.45   $121.40  
  Purchase #5 $102.92   13.690%   $117.0097   $117.01   $117.00   $117.00  
  Purchase #6 $66.67   11.292%   $74.1984   $74.20   $74.20   $74.20  
  Purchase #7 $188.52   8.793%   $205.0966   $205.10   $205.10   $205.10  
  7 purchase totals = $821.23       $898.7472   $898.76   $898.75   $898.70