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 $143.50   5.868%   $151.9206   $151.92   $151.90   $151.90  
  Purchase #2 $229.25   4.628%   $239.8597   $239.86   $239.85   $239.90  
  Purchase #3 $64.36   7.711%   $69.3228   $69.32   $69.30   $69.30  
  Purchase #4 $215.28   12.700%   $242.6206   $242.62   $242.60   $242.60  
  Purchase #5 $103.45   11.276%   $115.115   $115.12   $115.10   $115.10  
  Purchase #6 $23.62   5.173%   $24.8419   $24.84   $24.85   $24.80  
  Purchase #7 $114.92   4.274%   $119.8317   $119.83   $119.85   $119.80  
  7 purchase totals = $894.38       $963.5123   $963.51   $963.45   $963.40