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 $112.59   13.297%   $127.5611   $127.56   $127.55   $127.60  
  Purchase #2 $224.67   9.474%   $245.9552   $245.96   $245.95   $246.00  
  Purchase #3 $131.89   9.231%   $144.0648   $144.06   $144.05   $144.10  
  Purchase #4 $64.79   5.230%   $68.1785   $68.18   $68.20   $68.20  
  Purchase #5 $43.49   8.341%   $47.1175   $47.12   $47.10   $47.10  
  Purchase #6 $158.64   7.348%   $170.2969   $170.30   $170.30   $170.30  
  Purchase #7 $48.39   7.394%   $51.968   $51.97   $51.95   $52.00  
  7 purchase totals = $784.46       $855.1420   $855.15   $855.10   $855.30