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 $61.49   3.778%   $63.8131   $63.81   $63.80   $63.80  
  Purchase #2 $64.62   8.313%   $69.9919   $69.99   $70.00   $70.00  
  Purchase #3 $243.87   7.642%   $262.5065   $262.51   $262.50   $262.50  
  Purchase #4 $157.96   12.289%   $177.3717   $177.37   $177.35   $177.40  
  Purchase #5 $179.35   5.440%   $189.1066   $189.11   $189.10   $189.10  
  Purchase #6 $244.44   6.125%   $259.412   $259.41   $259.40   $259.40  
  Purchase #7 $242.63   3.222%   $250.4475   $250.45   $250.45   $250.40  
  7 purchase totals = $1,194.36       $1,272.6493   $1,272.65   $1,272.60   $1,272.60