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 $66.38   3.607%   $68.7743   $68.77   $68.75   $68.80  
  Purchase #2 $86.99   11.149%   $96.6885   $96.69   $96.70   $96.70  
  Purchase #3 $175.29   5.666%   $185.2219   $185.22   $185.20   $185.20  
  Purchase #4 $230.68   13.667%   $262.207   $262.21   $262.20   $262.20  
  Purchase #5 $39.98   6.783%   $42.6918   $42.69   $42.70   $42.70  
  Purchase #6 $101.71   9.561%   $111.4345   $111.43   $111.45   $111.40  
  Purchase #7 $214.87   6.360%   $228.5357   $228.54   $228.55   $228.50  
  7 purchase totals = $915.90       $995.5537   $995.55   $995.55   $995.50