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 $240.58   8.797%   $261.7438   $261.74   $261.75   $261.70  
  Purchase #2 $205.87   3.704%   $213.4954   $213.50   $213.50   $213.50  
  Purchase #3 $41.66   8.594%   $45.2403   $45.24   $45.25   $45.20  
  Purchase #4 $227.98   11.334%   $253.8193   $253.82   $253.80   $253.80  
  Purchase #5 $97.49   7.362%   $104.6672   $104.67   $104.65   $104.70  
  Purchase #6 $191.71   12.829%   $216.3045   $216.30   $216.30   $216.30  
  Purchase #7 $75.39   11.407%   $83.9897   $83.99   $84.00   $84.00  
  7 purchase totals = $1,080.68       $1,179.2602   $1,179.26   $1,179.25   $1,179.20