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 $135.29   12.121%   $151.6885   $151.69   $151.70   $151.70  
  Purchase #2 $31.40   12.445%   $35.3077   $35.31   $35.30   $35.30  
  Purchase #3 $91.34   6.664%   $97.4269   $97.43   $97.45   $97.40  
  Purchase #4 $54.87   12.406%   $61.6772   $61.68   $61.70   $61.70  
  Purchase #5 $149.84   11.700%   $167.3713   $167.37   $167.35   $167.40  
  Purchase #6 $172.76   13.198%   $195.5609   $195.56   $195.55   $195.60  
  Purchase #7 $87.67   5.145%   $92.1806   $92.18   $92.20   $92.20  
  7 purchase totals = $723.17       $801.2131   $801.22   $801.25   $801.30