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 $248.92   4.869%   $261.0399   $261.04   $261.05   $261.00  
  Purchase #2 $86.27   6.549%   $91.9198   $91.92   $91.90   $91.90  
  Purchase #3 $70.50   8.873%   $76.7555   $76.76   $76.75   $76.80  
  Purchase #4 $239.50   12.506%   $269.4519   $269.45   $269.45   $269.50  
  Purchase #5 $226.47   6.750%   $241.7567   $241.76   $241.75   $241.80  
  Purchase #6 $149.55   6.815%   $159.7418   $159.74   $159.75   $159.70  
  Purchase #7 $131.32   5.731%   $138.8459   $138.85   $138.85   $138.80  
  7 purchase totals = $1,152.53       $1,239.5115   $1,239.52   $1,239.50   $1,239.50