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 $73.98   13.115%   $83.6825   $83.68   $83.70   $83.70  
  Purchase #2 $142.68   6.416%   $151.8343   $151.83   $151.85   $151.80  
  Purchase #3 $154.27   10.792%   $170.9188   $170.92   $170.90   $170.90  
  Purchase #4 $122.39   6.460%   $130.2964   $130.30   $130.30   $130.30  
  Purchase #5 $200.72   6.610%   $213.9876   $213.99   $214.00   $214.00  
  Purchase #6 $99.81   11.163%   $110.9518   $110.95   $110.95   $111.00  
  Purchase #7 $82.50   9.457%   $90.302   $90.30   $90.30   $90.30  
  7 purchase totals = $876.35       $951.9734   $951.97   $952.00   $952.00