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 $234.61   13.326%   $265.8741   $265.87   $265.85   $265.90  
  Purchase #2 $221.37   8.644%   $240.5052   $240.51   $240.50   $240.50  
  Purchase #3 $149.57   8.263%   $161.929   $161.93   $161.95   $161.90  
  Purchase #4 $94.94   11.342%   $105.7081   $105.71   $105.70   $105.70  
  Purchase #5 $233.49   5.459%   $246.2362   $246.24   $246.25   $246.20  
  Purchase #6 $76.79   12.178%   $86.1415   $86.14   $86.15   $86.10  
  Purchase #7 $135.50   10.310%   $149.4701   $149.47   $149.45   $149.50  
  7 purchase totals = $1,146.27       $1,255.8642   $1,255.87   $1,255.85   $1,255.80