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 $60.52   8.633%   $65.7447   $65.74   $65.75   $65.70  
  Purchase #2 $103.32   5.424%   $108.9241   $108.92   $108.90   $108.90  
  Purchase #3 $58.90   8.618%   $63.976   $63.98   $64.00   $64.00  
  Purchase #4 $152.31   9.867%   $167.3384   $167.34   $167.35   $167.30  
  Purchase #5 $197.52   8.466%   $214.242   $214.24   $214.25   $214.20  
  Purchase #6 $193.63   3.650%   $200.6975   $200.70   $200.70   $200.70  
  Purchase #7 $119.96   8.690%   $130.3845   $130.38   $130.40   $130.40  
  7 purchase totals = $886.16       $951.3072   $951.30   $951.35   $951.20