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 $68.58   9.549%   $75.1287   $75.13   $75.15   $75.10  
  Purchase #2 $184.62   8.192%   $199.7441   $199.74   $199.75   $199.70  
  Purchase #3 $14.88   3.145%   $15.348   $15.35   $15.35   $15.30  
  Purchase #4 $23.61   4.488%   $24.6696   $24.67   $24.65   $24.70  
  Purchase #5 $185.72   10.461%   $205.1482   $205.15   $205.15   $205.10  
  Purchase #6 $189.67   3.621%   $196.538   $196.54   $196.55   $196.50  
  Purchase #7 $227.59   9.520%   $249.2566   $249.26   $249.25   $249.30  
  7 purchase totals = $894.67       $965.8332   $965.84   $965.85   $965.70