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 $229.97   13.309%   $260.5767   $260.58   $260.60   $260.60  
  Purchase #2 $103.57   8.219%   $112.0824   $112.08   $112.10   $112.10  
  Purchase #3 $108.35   5.238%   $114.0254   $114.03   $114.05   $114.00  
  Purchase #4 $119.67   4.424%   $124.9642   $124.96   $124.95   $125.00  
  Purchase #5 $193.49   7.809%   $208.5996   $208.60   $208.60   $208.60  
  Purchase #6 $89.26   4.530%   $93.3035   $93.30   $93.30   $93.30  
  Purchase #7 $32.39   13.242%   $36.6791   $36.68   $36.70   $36.70  
  7 purchase totals = $876.70       $950.2309   $950.23   $950.30   $950.30