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 $62.30   13.701%   $70.8357   $70.84   $70.85   $70.80  
  Purchase #2 $198.93   11.568%   $221.9422   $221.94   $221.95   $221.90  
  Purchase #3 $180.67   4.143%   $188.1552   $188.16   $188.15   $188.20  
  Purchase #4 $240.36   10.391%   $265.3358   $265.34   $265.35   $265.30  
  Purchase #5 $213.43   9.298%   $233.2747   $233.27   $233.25   $233.30  
  Purchase #6 $42.44   10.169%   $46.7557   $46.76   $46.75   $46.80  
  Purchase #7 $212.95   13.385%   $241.4534   $241.45   $241.45   $241.50  
  7 purchase totals = $1,151.08       $1,267.7527   $1,267.76   $1,267.75   $1,267.80