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 $41.26   12.861%   $46.5664   $46.57   $46.55   $46.60  
  Purchase #2 $209.94   8.871%   $228.5638   $228.56   $228.55   $228.60  
  Purchase #3 $34.53   8.287%   $37.3915   $37.39   $37.40   $37.40  
  Purchase #4 $139.32   10.744%   $154.2885   $154.29   $154.30   $154.30  
  Purchase #5 $154.56   10.294%   $170.4704   $170.47   $170.45   $170.50  
  Purchase #6 $235.62   10.630%   $260.6664   $260.67   $260.65   $260.70  
  Purchase #7 $206.93   7.256%   $221.9448   $221.94   $221.95   $221.90  
  7 purchase totals = $1,022.16       $1,119.8918   $1,119.89   $1,119.85   $1,120.00