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 $246.43   5.826%   $260.787   $260.79   $260.80   $260.80  
  Purchase #2 $15.57   11.656%   $17.3848   $17.38   $17.40   $17.40  
  Purchase #3 $123.94   7.634%   $133.4016   $133.40   $133.40   $133.40  
  Purchase #4 $158.52   3.811%   $164.5612   $164.56   $164.55   $164.60  
  Purchase #5 $200.38   7.605%   $215.6189   $215.62   $215.60   $215.60  
  Purchase #6 $242.74   3.433%   $251.0733   $251.07   $251.05   $251.10  
  Purchase #7 $194.95   6.359%   $207.3469   $207.35   $207.35   $207.30  
  7 purchase totals = $1,182.53       $1,250.1737   $1,250.17   $1,250.15   $1,250.20