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 $70.75   12.210%   $79.3886   $79.39   $79.40   $79.40  
  Purchase #2 $133.59   7.776%   $143.978   $143.98   $144.00   $144.00  
  Purchase #3 $28.69   8.489%   $31.1255   $31.13   $31.15   $31.10  
  Purchase #4 $18.32   3.345%   $18.9328   $18.93   $18.95   $18.90  
  Purchase #5 $99.68   3.736%   $103.404   $103.40   $103.40   $103.40  
  Purchase #6 $19.37   10.295%   $21.3641   $21.36   $21.35   $21.40  
  Purchase #7 $43.82   13.551%   $49.758   $49.76   $49.75   $49.80  
  7 purchase totals = $414.22       $447.9510   $447.95   $448.00   $448.00