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 $73.87   4.596%   $77.2651   $77.27   $77.25   $77.30  
  Purchase #2 $125.95   10.188%   $138.7818   $138.78   $138.80   $138.80  
  Purchase #3 $60.84   11.527%   $67.853   $67.85   $67.85   $67.90  
  Purchase #4 $180.29   6.357%   $191.751   $191.75   $191.75   $191.80  
  Purchase #5 $234.26   3.417%   $242.2647   $242.26   $242.25   $242.30  
  Purchase #6 $125.29   13.202%   $141.8308   $141.83   $141.85   $141.80  
  Purchase #7 $154.49   6.612%   $164.7049   $164.70   $164.70   $164.70  
  7 purchase totals = $954.99       $1,024.4513   $1,024.44   $1,024.45   $1,024.60