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 $68.44   7.249%   $73.4012   $73.40   $73.40   $73.40  
  Purchase #2 $93.91   12.192%   $105.3595   $105.36   $105.35   $105.40  
  Purchase #3 $202.47   7.439%   $217.5317   $217.53   $217.55   $217.50  
  Purchase #4 $157.56   13.108%   $178.213   $178.21   $178.20   $178.20  
  Purchase #5 $161.90   11.796%   $180.9977   $181.00   $181.00   $181.00  
  Purchase #6 $177.60   10.326%   $195.939   $195.94   $195.95   $195.90  
  Purchase #7 $103.43   12.312%   $116.1643   $116.16   $116.15   $116.20  
  7 purchase totals = $965.31       $1,067.6064   $1,067.60   $1,067.60   $1,067.60