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 $118.51   6.613%   $126.3471   $126.35   $126.35   $126.30  
  Purchase #2 $209.39   12.871%   $236.3406   $236.34   $236.35   $236.30  
  Purchase #3 $171.54   5.259%   $180.5613   $180.56   $180.55   $180.60  
  Purchase #4 $130.42   10.313%   $143.8702   $143.87   $143.85   $143.90  
  Purchase #5 $229.65   3.574%   $237.8577   $237.86   $237.85   $237.90  
  Purchase #6 $109.70   4.665%   $114.8175   $114.82   $114.80   $114.80  
  Purchase #7 $201.59   4.391%   $210.4418   $210.44   $210.45   $210.40  
  7 purchase totals = $1,170.80       $1,250.2362   $1,250.24   $1,250.20   $1,250.20