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 $48.56   4.240%   $50.6189   $50.62   $50.60   $50.60  
  Purchase #2 $24.58   11.325%   $27.3637   $27.36   $27.35   $27.40  
  Purchase #3 $235.85   3.526%   $244.1661   $244.17   $244.15   $244.20  
  Purchase #4 $224.58   5.749%   $237.4911   $237.49   $237.50   $237.50  
  Purchase #5 $109.57   11.794%   $122.4927   $122.49   $122.50   $122.50  
  Purchase #6 $46.82   13.276%   $53.0358   $53.04   $53.05   $53.00  
  Purchase #7 $202.38   11.476%   $225.6051   $225.61   $225.60   $225.60  
  7 purchase totals = $892.34       $960.7734   $960.78   $960.75   $960.80