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 $65.39   12.709%   $73.7004   $73.70   $73.70   $73.70  
  Purchase #2 $250.91   11.285%   $279.2252   $279.23   $279.25   $279.20  
  Purchase #3 $206.41   5.107%   $216.9514   $216.95   $216.95   $217.00  
  Purchase #4 $220.66   6.848%   $235.7708   $235.77   $235.75   $235.80  
  Purchase #5 $61.88   8.492%   $67.1348   $67.13   $67.15   $67.10  
  Purchase #6 $12.97   12.160%   $14.5472   $14.55   $14.55   $14.50  
  Purchase #7 $41.61   11.196%   $46.2687   $46.27   $46.25   $46.30  
  7 purchase totals = $859.83       $933.5985   $933.60   $933.60   $933.60