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 $39.79   3.790%   $41.298   $41.30   $41.30   $41.30  
  Purchase #2 $173.82   11.715%   $194.183   $194.18   $194.20   $194.20  
  Purchase #3 $183.40   13.117%   $207.4566   $207.46   $207.45   $207.50  
  Purchase #4 $149.26   5.677%   $157.7335   $157.73   $157.75   $157.70  
  Purchase #5 $21.27   11.635%   $23.7448   $23.74   $23.75   $23.70  
  Purchase #6 $241.41   9.675%   $264.7664   $264.77   $264.75   $264.80  
  Purchase #7 $146.59   12.482%   $164.8874   $164.89   $164.90   $164.90  
  7 purchase totals = $955.54       $1,054.0697   $1,054.07   $1,054.10   $1,054.10