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 $183.64   8.277%   $198.8399   $198.84   $198.85   $198.80  
  Purchase #2 $231.95   7.723%   $249.8635   $249.86   $249.85   $249.90  
  Purchase #3 $49.57   7.538%   $53.3066   $53.31   $53.30   $53.30  
  Purchase #4 $151.45   3.613%   $156.9219   $156.92   $156.90   $156.90  
  Purchase #5 $200.34   10.462%   $221.2996   $221.30   $221.30   $221.30  
  Purchase #6 $8.96   4.696%   $9.3808   $9.38   $9.40   $9.40  
  Purchase #7 $86.62   8.353%   $93.8554   $93.86   $93.85   $93.90  
  7 purchase totals = $912.53       $983.4677   $983.47   $983.45   $983.50