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 $54.65   4.792%   $57.2688   $57.27   $57.25   $57.30  
  Purchase #2 $86.92   11.627%   $97.0262   $97.03   $97.05   $97.00  
  Purchase #3 $154.45   12.734%   $174.1177   $174.12   $174.10   $174.10  
  Purchase #4 $16.76   13.428%   $19.0105   $19.01   $19.00   $19.00  
  Purchase #5 $161.92   9.645%   $177.5372   $177.54   $177.55   $177.50  
  Purchase #6 $203.86   7.743%   $219.6449   $219.64   $219.65   $219.60  
  Purchase #7 $186.34   8.771%   $202.6839   $202.68   $202.70   $202.70  
  7 purchase totals = $864.90       $947.2892   $947.29   $947.30   $947.20