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 $194.74   10.792%   $215.7563   $215.76   $215.75   $215.80  
  Purchase #2 $194.68   13.443%   $220.8508   $220.85   $220.85   $220.90  
  Purchase #3 $12.40   13.239%   $14.0416   $14.04   $14.05   $14.00  
  Purchase #4 $98.93   13.171%   $111.9601   $111.96   $111.95   $112.00  
  Purchase #5 $119.70   13.229%   $135.5351   $135.54   $135.55   $135.50  
  Purchase #6 $51.34   12.174%   $57.5901   $57.59   $57.60   $57.60  
  Purchase #7 $250.89   10.703%   $277.7428   $277.74   $277.75   $277.70  
  7 purchase totals = $922.68       $1,033.4768   $1,033.48   $1,033.50   $1,033.50