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 $82.94   12.475%   $93.2868   $93.29   $93.30   $93.30  
  Purchase #2 $229.45   10.287%   $253.0535   $253.05   $253.05   $253.10  
  Purchase #3 $37.49   7.143%   $40.1679   $40.17   $40.15   $40.20  
  Purchase #4 $104.88   7.629%   $112.8813   $112.88   $112.90   $112.90  
  Purchase #5 $111.55   7.342%   $119.74   $119.74   $119.75   $119.70  
  Purchase #6 $33.28   6.676%   $35.5018   $35.50   $35.50   $35.50  
  Purchase #7 $218.82   3.295%   $226.0301   $226.03   $226.05   $226.00  
  7 purchase totals = $818.41       $880.6614   $880.66   $880.70   $880.70