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 $187.34   3.827%   $194.5095   $194.51   $194.50   $194.50  
  Purchase #2 $178.42   11.277%   $198.5404   $198.54   $198.55   $198.50  
  Purchase #3 $95.94   11.428%   $106.904   $106.90   $106.90   $106.90  
  Purchase #4 $246.57   3.128%   $254.2827   $254.28   $254.30   $254.30  
  Purchase #5 $200.83   8.539%   $217.9789   $217.98   $218.00   $218.00  
  Purchase #6 $217.81   9.392%   $238.2667   $238.27   $238.25   $238.30  
  Purchase #7 $77.62   11.382%   $86.4547   $86.45   $86.45   $86.50  
  7 purchase totals = $1,204.53       $1,296.9369   $1,296.93   $1,296.95   $1,297.00