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 $108.55   10.170%   $119.5895   $119.59   $119.60   $119.60  
  Purchase #2 $121.72   12.276%   $136.6623   $136.66   $136.65   $136.70  
  Purchase #3 $180.99   7.640%   $194.8176   $194.82   $194.80   $194.80  
  Purchase #4 $195.99   12.659%   $220.8004   $220.80   $220.80   $220.80  
  Purchase #5 $15.36   13.789%   $17.478   $17.48   $17.50   $17.50  
  Purchase #6 $105.47   13.503%   $119.7116   $119.71   $119.70   $119.70  
  Purchase #7 $114.45   6.201%   $121.547   $121.55   $121.55   $121.50  
  7 purchase totals = $842.53       $930.6064   $930.61   $930.60   $930.60