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 $179.85   13.560%   $204.2377   $204.24   $204.25   $204.20  
  Purchase #2 $183.51   8.390%   $198.9065   $198.91   $198.90   $198.90  
  Purchase #3 $72.94   7.380%   $78.323   $78.32   $78.30   $78.30  
  Purchase #4 $212.66   13.485%   $241.3372   $241.34   $241.35   $241.30  
  Purchase #5 $86.79   5.774%   $91.8013   $91.80   $91.80   $91.80  
  Purchase #6 $229.53   11.175%   $255.18   $255.18   $255.20   $255.20  
  Purchase #7 $193.43   7.258%   $207.4691   $207.47   $207.45   $207.50  
  7 purchase totals = $1,158.71       $1,277.2548   $1,277.26   $1,277.25   $1,277.20