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 $94.62   5.351%   $99.6831   $99.68   $99.70   $99.70  
  Purchase #2 $191.94   5.464%   $202.4276   $202.43   $202.45   $202.40  
  Purchase #3 $119.71   9.441%   $131.0118   $131.01   $131.00   $131.00  
  Purchase #4 $42.88   7.824%   $46.2349   $46.23   $46.25   $46.20  
  Purchase #5 $185.78   13.604%   $211.0535   $211.05   $211.05   $211.10  
  Purchase #6 $53.39   10.521%   $59.0072   $59.01   $59.00   $59.00  
  Purchase #7 $61.80   6.163%   $65.6087   $65.61   $65.60   $65.60  
  7 purchase totals = $750.12       $815.0268   $815.02   $815.05   $815.00