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 $203.29   7.507%   $218.551   $218.55   $218.55   $218.60  
  Purchase #2 $102.25   4.687%   $107.0425   $107.04   $107.05   $107.00  
  Purchase #3 $86.79   7.552%   $93.3444   $93.34   $93.35   $93.30  
  Purchase #4 $62.71   6.452%   $66.756   $66.76   $66.75   $66.80  
  Purchase #5 $84.72   5.708%   $89.5558   $89.56   $89.55   $89.60  
  Purchase #6 $185.47   3.513%   $191.9856   $191.99   $192.00   $192.00  
  Purchase #7 $203.39   12.764%   $229.3507   $229.35   $229.35   $229.40  
  7 purchase totals = $928.62       $996.5860   $996.59   $996.60   $996.70