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 $117.25   4.803%   $122.8815   $122.88   $122.90   $122.90  
  Purchase #2 $33.92   13.103%   $38.3645   $38.36   $38.35   $38.40  
  Purchase #3 $89.90   9.214%   $98.1834   $98.18   $98.20   $98.20  
  Purchase #4 $237.92   5.617%   $251.284   $251.28   $251.30   $251.30  
  Purchase #5 $125.75   9.293%   $137.4359   $137.44   $137.45   $137.40  
  Purchase #6 $182.51   6.279%   $193.9698   $193.97   $193.95   $194.00  
  Purchase #7 $169.39   3.663%   $175.5948   $175.59   $175.60   $175.60  
  7 purchase totals = $956.64       $1,017.7139   $1,017.70   $1,017.75   $1,017.80