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 $61.84   8.291%   $66.9672   $66.97   $66.95   $67.00  
  Purchase #2 $90.59   6.445%   $96.4285   $96.43   $96.45   $96.40  
  Purchase #3 $48.82   7.219%   $52.3443   $52.34   $52.35   $52.30  
  Purchase #4 $201.66   4.381%   $210.4947   $210.49   $210.50   $210.50  
  Purchase #5 $124.61   6.323%   $132.4891   $132.49   $132.50   $132.50  
  Purchase #6 $26.58   11.436%   $29.6197   $29.62   $29.60   $29.60  
  Purchase #7 $213.33   11.443%   $237.7414   $237.74   $237.75   $237.70  
  7 purchase totals = $767.43       $826.0849   $826.08   $826.10   $826.00