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 $53.71   13.434%   $60.9254   $60.93   $60.95   $60.90  
  Purchase #2 $25.37   13.590%   $28.8178   $28.82   $28.80   $28.80  
  Purchase #3 $229.62   6.537%   $244.6303   $244.63   $244.65   $244.60  
  Purchase #4 $150.86   5.590%   $159.2931   $159.29   $159.30   $159.30  
  Purchase #5 $54.73   3.803%   $56.8114   $56.81   $56.80   $56.80  
  Purchase #6 $105.55   4.441%   $110.2375   $110.24   $110.25   $110.20  
  Purchase #7 $32.59   13.614%   $37.0268   $37.03   $37.05   $37.00  
  7 purchase totals = $652.43       $697.7423   $697.75   $697.80   $697.60