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 $8.43   8.477%   $9.1446   $9.14   $9.15   $9.10  
  Purchase #2 $25.46   10.284%   $28.0783   $28.08   $28.10   $28.10  
  Purchase #3 $219.94   4.620%   $230.1012   $230.10   $230.10   $230.10  
  Purchase #4 $247.30   6.634%   $263.7059   $263.71   $263.70   $263.70  
  Purchase #5 $186.41   7.264%   $199.9508   $199.95   $199.95   $200.00  
  Purchase #6 $152.88   5.664%   $161.5391   $161.54   $161.55   $161.50  
  Purchase #7 $88.58   9.579%   $97.0651   $97.07   $97.05   $97.10  
  7 purchase totals = $929.00       $989.5850   $989.59   $989.60   $989.60