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 $46.85   3.593%   $48.5333   $48.53   $48.55   $48.50  
  Purchase #2 $176.95   9.488%   $193.739   $193.74   $193.75   $193.70  
  Purchase #3 $126.25   13.719%   $143.5702   $143.57   $143.55   $143.60  
  Purchase #4 $240.72   13.296%   $272.7261   $272.73   $272.75   $272.70  
  Purchase #5 $78.43   8.250%   $84.9005   $84.90   $84.90   $84.90  
  Purchase #6 $81.61   8.248%   $88.3412   $88.34   $88.35   $88.30  
  Purchase #7 $81.81   9.591%   $89.6564   $89.66   $89.65   $89.70  
  7 purchase totals = $832.62       $921.4667   $921.47   $921.50   $921.40