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 $126.44   5.631%   $133.5598   $133.56   $133.55   $133.60  
  Purchase #2 $25.42   10.668%   $28.1318   $28.13   $28.15   $28.10  
  Purchase #3 $163.80   5.754%   $173.2251   $173.23   $173.25   $173.20  
  Purchase #4 $24.39   10.777%   $27.0185   $27.02   $27.00   $27.00  
  Purchase #5 $198.59   3.333%   $205.209   $205.21   $205.20   $205.20  
  Purchase #6 $62.58   10.758%   $69.3124   $69.31   $69.30   $69.30  
  Purchase #7 $158.59   4.554%   $165.8122   $165.81   $165.80   $165.80  
  7 purchase totals = $759.81       $802.2688   $802.27   $802.25   $802.20