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 $93.68   11.805%   $104.7389   $104.74   $104.75   $104.70  
  Purchase #2 $138.36   11.233%   $153.902   $153.90   $153.90   $153.90  
  Purchase #3 $40.36   12.673%   $45.4748   $45.47   $45.45   $45.50  
  Purchase #4 $24.53   7.335%   $26.3293   $26.33   $26.35   $26.30  
  Purchase #5 $197.42   4.690%   $206.679   $206.68   $206.70   $206.70  
  Purchase #6 $10.65   12.127%   $11.9415   $11.94   $11.95   $11.90  
  Purchase #7 $97.34   5.269%   $102.4688   $102.47   $102.45   $102.50  
  7 purchase totals = $602.34       $651.5343   $651.53   $651.55   $651.50