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 $65.88   12.122%   $73.866   $73.87   $73.85   $73.90  
  Purchase #2 $109.62   9.755%   $120.3134   $120.31   $120.30   $120.30  
  Purchase #3 $73.45   7.549%   $78.9947   $78.99   $79.00   $79.00  
  Purchase #4 $119.38   13.747%   $135.7912   $135.79   $135.80   $135.80  
  Purchase #5 $230.45   6.269%   $244.8969   $244.90   $244.90   $244.90  
  Purchase #6 $166.37   11.346%   $185.2463   $185.25   $185.25   $185.20  
  Purchase #7 $11.88   7.874%   $12.8154   $12.82   $12.80   $12.80  
  7 purchase totals = $777.03       $851.9239   $851.93   $851.90   $851.90