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 $182.68   6.466%   $194.4921   $194.49   $194.50   $194.50  
  Purchase #2 $217.95   11.435%   $242.8726   $242.87   $242.85   $242.90  
  Purchase #3 $168.25   4.225%   $175.3586   $175.36   $175.35   $175.40  
  Purchase #4 $104.74   11.866%   $117.1684   $117.17   $117.15   $117.20  
  Purchase #5 $64.43   9.581%   $70.603   $70.60   $70.60   $70.60  
  Purchase #6 $60.56   7.705%   $65.2261   $65.23   $65.25   $65.20  
  Purchase #7 $116.72   3.360%   $120.6418   $120.64   $120.65   $120.60  
  7 purchase totals = $915.33       $986.3626   $986.36   $986.35   $986.40