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 $57.73   8.469%   $62.6192   $62.62   $62.60   $62.60  
  Purchase #2 $191.95   9.567%   $210.3139   $210.31   $210.30   $210.30  
  Purchase #3 $74.43   7.350%   $79.9006   $79.90   $79.90   $79.90  
  Purchase #4 $227.49   12.823%   $256.661   $256.66   $256.65   $256.70  
  Purchase #5 $232.44   12.615%   $261.7623   $261.76   $261.75   $261.80  
  Purchase #6 $173.26   6.561%   $184.6276   $184.63   $184.65   $184.60  
  Purchase #7 $189.98   10.539%   $210.002   $210.00   $210.00   $210.00  
  7 purchase totals = $1,147.28       $1,265.8866   $1,265.88   $1,265.85   $1,265.90