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 $158.57   10.552%   $175.3023   $175.30   $175.30   $175.30  
  Purchase #2 $50.99   9.763%   $55.9682   $55.97   $55.95   $56.00  
  Purchase #3 $66.92   5.169%   $70.3791   $70.38   $70.40   $70.40  
  Purchase #4 $132.86   4.355%   $138.6461   $138.65   $138.65   $138.60  
  Purchase #5 $249.51   6.624%   $266.0375   $266.04   $266.05   $266.00  
  Purchase #6 $68.42   7.472%   $73.5323   $73.53   $73.55   $73.50  
  Purchase #7 $227.81   9.759%   $250.042   $250.04   $250.05   $250.00  
  7 purchase totals = $955.08       $1,029.9075   $1,029.91   $1,029.95   $1,029.80