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 $45.39   5.841%   $48.0412   $48.04   $48.05   $48.00  
  Purchase #2 $60.60   12.192%   $67.9884   $67.99   $68.00   $68.00  
  Purchase #3 $46.57   6.872%   $49.7703   $49.77   $49.75   $49.80  
  Purchase #4 $210.56   9.834%   $231.2665   $231.27   $231.25   $231.30  
  Purchase #5 $130.69   8.129%   $141.3138   $141.31   $141.30   $141.30  
  Purchase #6 $111.54   11.407%   $124.2634   $124.26   $124.25   $124.30  
  Purchase #7 $250.90   6.546%   $267.3239   $267.32   $267.30   $267.30  
  7 purchase totals = $856.25       $929.9675   $929.96   $929.90   $930.00