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 $105.80   12.407%   $118.9266   $118.93   $118.95   $118.90  
  Purchase #2 $197.99   10.241%   $218.2662   $218.27   $218.25   $218.30  
  Purchase #3 $222.31   6.858%   $237.556   $237.56   $237.55   $237.60  
  Purchase #4 $126.42   4.739%   $132.411   $132.41   $132.40   $132.40  
  Purchase #5 $172.80   6.653%   $184.2964   $184.30   $184.30   $184.30  
  Purchase #6 $62.31   7.381%   $66.9091   $66.91   $66.90   $66.90  
  Purchase #7 $52.49   7.159%   $56.2478   $56.25   $56.25   $56.20  
  7 purchase totals = $940.12       $1,014.6131   $1,014.63   $1,014.60   $1,014.60