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 $105.84   12.280%   $118.8372   $118.84   $118.85   $118.80  
  Purchase #2 $86.97   6.328%   $92.4735   $92.47   $92.45   $92.50  
  Purchase #3 $202.37   6.834%   $216.2   $216.20   $216.20   $216.20  
  Purchase #4 $151.79   6.451%   $161.582   $161.58   $161.60   $161.60  
  Purchase #5 $160.73   10.680%   $177.896   $177.90   $177.90   $177.90  
  Purchase #6 $117.40   13.635%   $133.4075   $133.41   $133.40   $133.40  
  Purchase #7 $102.64   3.681%   $106.4182   $106.42   $106.40   $106.40  
  7 purchase totals = $927.74       $1,006.8144   $1,006.82   $1,006.80   $1,006.80