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 $125.36   11.402%   $139.6535   $139.65   $139.65   $139.70  
  Purchase #2 $98.98   11.459%   $110.3221   $110.32   $110.30   $110.30  
  Purchase #3 $76.53   12.507%   $86.1016   $86.10   $86.10   $86.10  
  Purchase #4 $213.58   13.183%   $241.7363   $241.74   $241.75   $241.70  
  Purchase #5 $123.81   11.369%   $137.886   $137.89   $137.90   $137.90  
  Purchase #6 $74.28   9.687%   $81.4755   $81.48   $81.50   $81.50  
  Purchase #7 $135.47   10.761%   $150.0479   $150.05   $150.05   $150.00  
  7 purchase totals = $848.01       $947.2229   $947.23   $947.25   $947.20