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 $207.70   8.741%   $225.8551   $225.86   $225.85   $225.90  
  Purchase #2 $220.34   12.178%   $247.173   $247.17   $247.15   $247.20  
  Purchase #3 $236.63   6.407%   $251.7909   $251.79   $251.80   $251.80  
  Purchase #4 $165.90   5.680%   $175.3231   $175.32   $175.30   $175.30  
  Purchase #5 $219.35   8.240%   $237.4244   $237.42   $237.40   $237.40  
  Purchase #6 $55.83   6.167%   $59.273   $59.27   $59.25   $59.30  
  Purchase #7 $85.64   7.639%   $92.182   $92.18   $92.20   $92.20  
  7 purchase totals = $1,191.39       $1,289.0215   $1,289.01   $1,288.95   $1,289.10