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 $65.68   12.201%   $73.6936   $73.69   $73.70   $73.70  
  Purchase #2 $46.37   7.414%   $49.8079   $49.81   $49.80   $49.80  
  Purchase #3 $237.28   11.634%   $264.8852   $264.89   $264.90   $264.90  
  Purchase #4 $118.76   9.380%   $129.8997   $129.90   $129.90   $129.90  
  Purchase #5 $83.57   3.340%   $86.3612   $86.36   $86.35   $86.40  
  Purchase #6 $131.94   6.250%   $140.1863   $140.19   $140.20   $140.20  
  Purchase #7 $208.95   6.256%   $222.0219   $222.02   $222.00   $222.00  
  7 purchase totals = $892.55       $966.8558   $966.86   $966.85   $966.90