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 $67.93   7.761%   $73.202   $73.20   $73.20   $73.20  
  Purchase #2 $136.90   9.329%   $149.6714   $149.67   $149.65   $149.70  
  Purchase #3 $244.93   12.362%   $275.2082   $275.21   $275.20   $275.20  
  Purchase #4 $140.82   12.606%   $158.5718   $158.57   $158.55   $158.60  
  Purchase #5 $245.42   4.601%   $256.7118   $256.71   $256.70   $256.70  
  Purchase #6 $207.55   3.314%   $214.4282   $214.43   $214.45   $214.40  
  Purchase #7 $231.98   9.254%   $253.4474   $253.45   $253.45   $253.40  
  7 purchase totals = $1,275.53       $1,381.2408   $1,381.24   $1,381.20   $1,381.20