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 $148.54   3.341%   $153.5027   $153.50   $153.50   $153.50  
  Purchase #2 $229.51   13.873%   $261.3499   $261.35   $261.35   $261.30  
  Purchase #3 $16.87   13.399%   $19.1304   $19.13   $19.15   $19.10  
  Purchase #4 $158.57   11.547%   $176.8801   $176.88   $176.90   $176.90  
  Purchase #5 $50.45   4.263%   $52.6007   $52.60   $52.60   $52.60  
  Purchase #6 $140.70   4.430%   $146.933   $146.93   $146.95   $146.90  
  Purchase #7 $122.26   13.220%   $138.4228   $138.42   $138.40   $138.40  
  7 purchase totals = $866.90       $948.8196   $948.81   $948.85   $948.70