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 $212.29   4.255%   $221.3229   $221.32   $221.30   $221.30  
  Purchase #2 $65.69   12.542%   $73.9288   $73.93   $73.95   $73.90  
  Purchase #3 $61.69   9.138%   $67.3272   $67.33   $67.35   $67.30  
  Purchase #4 $108.61   11.666%   $121.2804   $121.28   $121.30   $121.30  
  Purchase #5 $189.60   6.708%   $202.3184   $202.32   $202.30   $202.30  
  Purchase #6 $197.79   10.622%   $218.7993   $218.80   $218.80   $218.80  
  Purchase #7 $54.67   4.269%   $57.0039   $57.00   $57.00   $57.00  
  7 purchase totals = $890.34       $961.9809   $961.98   $962.00   $961.90