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 $22.92   13.217%   $25.9493   $25.95   $25.95   $25.90  
  Purchase #2 $112.94   10.167%   $124.4226   $124.42   $124.40   $124.40  
  Purchase #3 $99.44   3.118%   $102.5405   $102.54   $102.55   $102.50  
  Purchase #4 $45.72   13.125%   $51.7208   $51.72   $51.70   $51.70  
  Purchase #5 $210.56   6.203%   $223.621   $223.62   $223.60   $223.60  
  Purchase #6 $117.74   8.141%   $127.3252   $127.33   $127.35   $127.30  
  Purchase #7 $93.31   9.216%   $101.9094   $101.91   $101.90   $101.90  
  7 purchase totals = $702.63       $757.4888   $757.49   $757.45   $757.30