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 $92.74   9.792%   $101.8211   $101.82   $101.80   $101.80  
  Purchase #2 $143.38   5.369%   $151.0781   $151.08   $151.10   $151.10  
  Purchase #3 $87.26   11.489%   $97.2853   $97.29   $97.30   $97.30  
  Purchase #4 $231.83   13.677%   $263.5374   $263.54   $263.55   $263.50  
  Purchase #5 $209.98   9.230%   $229.3612   $229.36   $229.35   $229.40  
  Purchase #6 $59.46   8.623%   $64.5872   $64.59   $64.60   $64.60  
  Purchase #7 $21.68   7.531%   $23.3127   $23.31   $23.30   $23.30  
  7 purchase totals = $846.33       $930.9830   $930.99   $931.00   $931.00