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 $239.76   5.771%   $253.5965   $253.60   $253.60   $253.60  
  Purchase #2 $5.39   11.517%   $6.0108   $6.01   $6.00   $6.00  
  Purchase #3 $89.62   6.513%   $95.457   $95.46   $95.45   $95.50  
  Purchase #4 $172.31   3.457%   $178.2668   $178.27   $178.25   $178.30  
  Purchase #5 $241.57   13.292%   $273.6795   $273.68   $273.70   $273.70  
  Purchase #6 $65.51   11.658%   $73.1472   $73.15   $73.15   $73.10  
  Purchase #7 $247.73   10.526%   $273.8061   $273.81   $273.80   $273.80  
  7 purchase totals = $1,061.89       $1,153.9639   $1,153.98   $1,153.95   $1,154.00