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 $134.51   10.735%   $148.9496   $148.95   $148.95   $148.90  
  Purchase #2 $24.93   9.749%   $27.3604   $27.36   $27.35   $27.40  
  Purchase #3 $224.49   9.136%   $244.9994   $245.00   $245.00   $245.00  
  Purchase #4 $94.73   9.708%   $103.9264   $103.93   $103.95   $103.90  
  Purchase #5 $44.33   13.262%   $50.209   $50.21   $50.20   $50.20  
  Purchase #6 $59.68   6.642%   $63.6439   $63.64   $63.65   $63.60  
  Purchase #7 $53.97   3.791%   $56.016   $56.02   $56.00   $56.00  
  7 purchase totals = $636.64       $695.1047   $695.11   $695.10   $695.00