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 $21.74   7.482%   $23.3666   $23.37   $23.35   $23.40  
  Purchase #2 $100.76   5.370%   $106.1708   $106.17   $106.15   $106.20  
  Purchase #3 $128.53   12.305%   $144.3456   $144.35   $144.35   $144.30  
  Purchase #4 $200.76   12.753%   $226.3629   $226.36   $226.35   $226.40  
  Purchase #5 $104.99   13.317%   $118.9715   $118.97   $118.95   $119.00  
  Purchase #6 $98.95   10.249%   $109.0914   $109.09   $109.10   $109.10  
  Purchase #7 $110.32   4.531%   $115.3186   $115.32   $115.30   $115.30  
  7 purchase totals = $766.05       $843.6274   $843.63   $843.55   $843.70