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 $249.71   10.619%   $276.2267   $276.23   $276.25   $276.20  
  Purchase #2 $220.93   5.263%   $232.5575   $232.56   $232.55   $232.60  
  Purchase #3 $57.99   5.464%   $61.1586   $61.16   $61.15   $61.20  
  Purchase #4 $152.58   4.843%   $159.9694   $159.97   $159.95   $160.00  
  Purchase #5 $224.79   7.575%   $241.8178   $241.82   $241.80   $241.80  
  Purchase #6 $73.81   10.149%   $81.301   $81.30   $81.30   $81.30  
  Purchase #7 $48.55   6.235%   $51.5771   $51.58   $51.60   $51.60  
  7 purchase totals = $1,028.36       $1,104.6081   $1,104.62   $1,104.60   $1,104.70