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 $189.41   8.331%   $205.1897   $205.19   $205.20   $205.20  
  Purchase #2 $112.90   11.534%   $125.9219   $125.92   $125.90   $125.90  
  Purchase #3 $60.68   7.326%   $65.1254   $65.13   $65.15   $65.10  
  Purchase #4 $22.78   5.202%   $23.965   $23.97   $23.95   $24.00  
  Purchase #5 $104.60   6.418%   $111.3132   $111.31   $111.30   $111.30  
  Purchase #6 $231.48   8.734%   $251.6975   $251.70   $251.70   $251.70  
  Purchase #7 $160.36   9.531%   $175.6439   $175.64   $175.65   $175.60  
  7 purchase totals = $882.21       $958.8566   $958.86   $958.85   $958.80