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 $59.35   13.733%   $67.5005   $67.50   $67.50   $67.50  
  Purchase #2 $216.62   6.604%   $230.9256   $230.93   $230.95   $230.90  
  Purchase #3 $170.97   6.740%   $182.4934   $182.49   $182.50   $182.50  
  Purchase #4 $116.60   5.662%   $123.2019   $123.20   $123.20   $123.20  
  Purchase #5 $199.87   10.552%   $220.9603   $220.96   $220.95   $221.00  
  Purchase #6 $195.38   9.746%   $214.4217   $214.42   $214.40   $214.40  
  Purchase #7 $36.64   5.509%   $38.6585   $38.66   $38.65   $38.70  
  7 purchase totals = $995.43       $1,078.1619   $1,078.16   $1,078.15   $1,078.20