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 $244.89   8.197%   $264.9636   $264.96   $264.95   $265.00  
  Purchase #2 $66.81   6.514%   $71.162   $71.16   $71.15   $71.20  
  Purchase #3 $234.71   13.457%   $266.2949   $266.29   $266.30   $266.30  
  Purchase #4 $198.79   11.650%   $221.949   $221.95   $221.95   $221.90  
  Purchase #5 $71.86   8.353%   $77.8625   $77.86   $77.85   $77.90  
  Purchase #6 $32.74   7.747%   $35.2764   $35.28   $35.30   $35.30  
  Purchase #7 $31.71   9.296%   $34.6578   $34.66   $34.65   $34.70  
  7 purchase totals = $881.51       $972.1662   $972.16   $972.15   $972.30