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 $155.43   10.562%   $171.8465   $171.85   $171.85   $171.80  
  Purchase #2 $185.99   10.397%   $205.3274   $205.33   $205.35   $205.30  
  Purchase #3 $210.25   11.571%   $234.578   $234.58   $234.60   $234.60  
  Purchase #4 $111.95   11.621%   $124.9597   $124.96   $124.95   $125.00  
  Purchase #5 $90.71   8.338%   $98.2734   $98.27   $98.25   $98.30  
  Purchase #6 $54.93   10.663%   $60.7872   $60.79   $60.80   $60.80  
  Purchase #7 $29.46   3.576%   $30.5135   $30.51   $30.50   $30.50  
  7 purchase totals = $838.72       $926.2857   $926.29   $926.30   $926.30