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 $62.34   7.330%   $66.9095   $66.91   $66.90   $66.90  
  Purchase #2 $48.29   3.307%   $49.887   $49.89   $49.90   $49.90  
  Purchase #3 $221.71   6.347%   $235.7819   $235.78   $235.80   $235.80  
  Purchase #4 $11.77   6.141%   $12.4928   $12.49   $12.50   $12.50  
  Purchase #5 $127.39   8.701%   $138.4742   $138.47   $138.45   $138.50  
  Purchase #6 $195.50   5.348%   $205.9553   $205.96   $205.95   $206.00  
  Purchase #7 $227.29   8.218%   $245.9687   $245.97   $245.95   $246.00  
  7 purchase totals = $894.29       $955.4694   $955.47   $955.45   $955.60