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 $89.39   6.423%   $95.1315   $95.13   $95.15   $95.10  
  Purchase #2 $245.82   9.814%   $269.9448   $269.94   $269.95   $269.90  
  Purchase #3 $135.66   4.142%   $141.279   $141.28   $141.30   $141.30  
  Purchase #4 $108.38   11.141%   $120.4546   $120.45   $120.45   $120.50  
  Purchase #5 $183.58   5.617%   $193.8917   $193.89   $193.90   $193.90  
  Purchase #6 $228.28   13.767%   $259.7073   $259.71   $259.70   $259.70  
  Purchase #7 $205.76   4.837%   $215.7126   $215.71   $215.70   $215.70  
  7 purchase totals = $1,196.87       $1,296.1215   $1,296.11   $1,296.15   $1,296.10