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 $83.81   13.102%   $94.7908   $94.79   $94.80   $94.80  
  Purchase #2 $101.94   8.835%   $110.9464   $110.95   $110.95   $110.90  
  Purchase #3 $100.47   9.556%   $110.0709   $110.07   $110.05   $110.10  
  Purchase #4 $72.59   4.836%   $76.1005   $76.10   $76.10   $76.10  
  Purchase #5 $71.32   3.266%   $73.6493   $73.65   $73.65   $73.60  
  Purchase #6 $150.64   12.552%   $169.5483   $169.55   $169.55   $169.50  
  Purchase #7 $160.53   4.283%   $167.4055   $167.41   $167.40   $167.40  
  7 purchase totals = $741.30       $802.5117   $802.52   $802.50   $802.40