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 $51.82   13.558%   $58.8458   $58.85   $58.85   $58.80  
  Purchase #2 $215.62   13.382%   $244.4743   $244.47   $244.45   $244.50  
  Purchase #3 $15.93   6.406%   $16.9505   $16.95   $16.95   $17.00  
  Purchase #4 $195.64   9.329%   $213.8913   $213.89   $213.90   $213.90  
  Purchase #5 $172.47   4.785%   $180.7227   $180.72   $180.70   $180.70  
  Purchase #6 $168.66   10.266%   $185.9746   $185.97   $185.95   $186.00  
  Purchase #7 $154.70   8.416%   $167.7196   $167.72   $167.70   $167.70  
  7 purchase totals = $974.84       $1,068.5788   $1,068.57   $1,068.50   $1,068.60