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 $23.90   10.233%   $26.3457   $26.35   $26.35   $26.30  
  Purchase #2 $52.94   7.842%   $57.0916   $57.09   $57.10   $57.10  
  Purchase #3 $246.86   3.350%   $255.1298   $255.13   $255.15   $255.10  
  Purchase #4 $178.32   11.149%   $198.2009   $198.20   $198.20   $198.20  
  Purchase #5 $246.65   13.196%   $279.1979   $279.20   $279.20   $279.20  
  Purchase #6 $25.33   4.109%   $26.3708   $26.37   $26.35   $26.40  
  Purchase #7 $179.75   5.856%   $190.2762   $190.28   $190.30   $190.30  
  7 purchase totals = $953.75       $1,032.6129   $1,032.62   $1,032.65   $1,032.60