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 $98.62   13.839%   $112.268   $112.27   $112.25   $112.30  
  Purchase #2 $245.29   6.775%   $261.9084   $261.91   $261.90   $261.90  
  Purchase #3 $176.62   10.615%   $195.3682   $195.37   $195.35   $195.40  
  Purchase #4 $56.94   7.307%   $61.1006   $61.10   $61.10   $61.10  
  Purchase #5 $12.28   10.133%   $13.5243   $13.52   $13.50   $13.50  
  Purchase #6 $102.90   4.165%   $107.1858   $107.19   $107.20   $107.20  
  Purchase #7 $241.52   12.443%   $271.5723   $271.57   $271.55   $271.60  
  7 purchase totals = $934.17       $1,022.9276   $1,022.93   $1,022.85   $1,023.00