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 $223.96   11.648%   $250.0469   $250.05   $250.05   $250.00  
  Purchase #2 $34.98   3.571%   $36.2291   $36.23   $36.25   $36.20  
  Purchase #3 $177.88   11.283%   $197.9502   $197.95   $197.95   $198.00  
  Purchase #4 $192.71   3.187%   $198.8517   $198.85   $198.85   $198.90  
  Purchase #5 $74.44   13.544%   $84.5222   $84.52   $84.50   $84.50  
  Purchase #6 $33.37   11.427%   $37.1832   $37.18   $37.20   $37.20  
  Purchase #7 $85.40   13.486%   $96.917   $96.92   $96.90   $96.90  
  7 purchase totals = $822.74       $901.7003   $901.70   $901.70   $901.70