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 $42.47   10.547%   $46.9493   $46.95   $46.95   $46.90  
  Purchase #2 $125.29   13.291%   $141.9423   $141.94   $141.95   $141.90  
  Purchase #3 $12.41   12.856%   $14.0054   $14.01   $14.00   $14.00  
  Purchase #4 $184.46   12.151%   $206.8737   $206.87   $206.85   $206.90  
  Purchase #5 $6.50   11.779%   $7.2656   $7.27   $7.25   $7.30  
  Purchase #6 $55.51   11.319%   $61.7932   $61.79   $61.80   $61.80  
  Purchase #7 $12.54   12.279%   $14.0798   $14.08   $14.10   $14.10  
  7 purchase totals = $439.18       $492.9093   $492.91   $492.90   $492.90