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 $35.66   3.581%   $36.937   $36.94   $36.95   $36.90  
  Purchase #2 $84.52   9.282%   $92.3651   $92.37   $92.35   $92.40  
  Purchase #3 $19.62   4.659%   $20.5341   $20.53   $20.55   $20.50  
  Purchase #4 $213.61   8.869%   $232.5551   $232.56   $232.55   $232.60  
  Purchase #5 $13.32   11.130%   $14.8025   $14.80   $14.80   $14.80  
  Purchase #6 $195.91   5.568%   $206.8183   $206.82   $206.80   $206.80  
  Purchase #7 $250.56   11.338%   $278.9685   $278.97   $278.95   $279.00  
  7 purchase totals = $813.20       $882.9806   $882.99   $882.95   $883.00