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 $211.97   13.790%   $241.2007   $241.20   $241.20   $241.20  
  Purchase #2 $95.56   10.210%   $105.3167   $105.32   $105.30   $105.30  
  Purchase #3 $159.49   8.786%   $173.5028   $173.50   $173.50   $173.50  
  Purchase #4 $66.33   7.352%   $71.2066   $71.21   $71.20   $71.20  
  Purchase #5 $28.34   6.453%   $30.1688   $30.17   $30.15   $30.20  
  Purchase #6 $11.75   7.687%   $12.6532   $12.65   $12.65   $12.70  
  Purchase #7 $186.75   10.294%   $205.974   $205.97   $205.95   $206.00  
  7 purchase totals = $760.19       $840.0228   $840.02   $839.95   $840.10