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 $245.88   7.473%   $264.2546   $264.25   $264.25   $264.30  
  Purchase #2 $139.90   9.613%   $153.3486   $153.35   $153.35   $153.30  
  Purchase #3 $196.70   8.123%   $212.6779   $212.68   $212.70   $212.70  
  Purchase #4 $234.46   9.854%   $257.5637   $257.56   $257.55   $257.60  
  Purchase #5 $123.71   12.480%   $139.149   $139.15   $139.15   $139.10  
  Purchase #6 $170.87   12.249%   $191.7999   $191.80   $191.80   $191.80  
  Purchase #7 $133.35   11.729%   $148.9906   $148.99   $149.00   $149.00  
  7 purchase totals = $1,244.87       $1,367.7843   $1,367.78   $1,367.80   $1,367.80