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 $232.87   5.772%   $246.3113   $246.31   $246.30   $246.30  
  Purchase #2 $71.84   3.556%   $74.3946   $74.39   $74.40   $74.40  
  Purchase #3 $21.95   6.402%   $23.3552   $23.36   $23.35   $23.40  
  Purchase #4 $159.87   6.444%   $170.172   $170.17   $170.15   $170.20  
  Purchase #5 $93.57   6.460%   $99.6146   $99.61   $99.60   $99.60  
  Purchase #6 $119.91   8.802%   $130.4645   $130.46   $130.45   $130.50  
  Purchase #7 $66.51   8.445%   $72.1268   $72.13   $72.15   $72.10  
  7 purchase totals = $766.52       $816.4390   $816.43   $816.40   $816.50