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 $234.79   7.769%   $253.0308   $253.03   $253.05   $253.00  
  Purchase #2 $69.40   13.612%   $78.8467   $78.85   $78.85   $78.80  
  Purchase #3 $38.61   4.739%   $40.4397   $40.44   $40.45   $40.40  
  Purchase #4 $208.72   11.824%   $233.3991   $233.40   $233.40   $233.40  
  Purchase #5 $226.81   6.709%   $242.0267   $242.03   $242.05   $242.00  
  Purchase #6 $183.45   7.766%   $197.6967   $197.70   $197.70   $197.70  
  Purchase #7 $12.96   12.253%   $14.548   $14.55   $14.55   $14.50  
  7 purchase totals = $974.74       $1,059.9877   $1,060.00   $1,060.05   $1,059.80