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 $182.96   10.363%   $201.9201   $201.92   $201.90   $201.90  
  Purchase #2 $131.92   5.168%   $138.7376   $138.74   $138.75   $138.70  
  Purchase #3 $137.64   8.179%   $148.8976   $148.90   $148.90   $148.90  
  Purchase #4 $34.97   6.429%   $37.2182   $37.22   $37.20   $37.20  
  Purchase #5 $117.59   6.854%   $125.6496   $125.65   $125.65   $125.60  
  Purchase #6 $97.45   8.844%   $106.0685   $106.07   $106.05   $106.10  
  Purchase #7 $191.83   3.619%   $198.7723   $198.77   $198.75   $198.80  
  7 purchase totals = $894.36       $957.2639   $957.27   $957.20   $957.20