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 $22.47   13.349%   $25.4695   $25.47   $25.45   $25.50  
  Purchase #2 $247.98   6.541%   $264.2004   $264.20   $264.20   $264.20  
  Purchase #3 $194.99   10.817%   $216.0821   $216.08   $216.10   $216.10  
  Purchase #4 $49.99   3.200%   $51.5897   $51.59   $51.60   $51.60  
  Purchase #5 $50.54   7.864%   $54.5145   $54.51   $54.50   $54.50  
  Purchase #6 $119.83   5.380%   $126.2769   $126.28   $126.30   $126.30  
  Purchase #7 $41.38   13.766%   $47.0764   $47.08   $47.10   $47.10  
  7 purchase totals = $727.18       $785.2095   $785.21   $785.25   $785.30