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 $56.72   6.597%   $60.4618   $60.46   $60.45   $60.50  
  Purchase #2 $195.48   5.489%   $206.2099   $206.21   $206.20   $206.20  
  Purchase #3 $213.61   13.155%   $241.7104   $241.71   $241.70   $241.70  
  Purchase #4 $162.74   8.283%   $176.2198   $176.22   $176.20   $176.20  
  Purchase #5 $106.54   11.668%   $118.9711   $118.97   $118.95   $119.00  
  Purchase #6 $23.30   12.340%   $26.1752   $26.18   $26.20   $26.20  
  Purchase #7 $248.93   8.404%   $269.8501   $269.85   $269.85   $269.90  
  7 purchase totals = $1,007.32       $1,099.5983   $1,099.60   $1,099.55   $1,099.70