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 $89.80   6.582%   $95.7106   $95.71   $95.70   $95.70  
  Purchase #2 $159.90   12.851%   $180.4487   $180.45   $180.45   $180.40  
  Purchase #3 $204.31   11.169%   $227.1294   $227.13   $227.15   $227.10  
  Purchase #4 $199.30   10.197%   $219.6226   $219.62   $219.60   $219.60  
  Purchase #5 $27.63   5.862%   $29.2497   $29.25   $29.25   $29.20  
  Purchase #6 $186.76   3.135%   $192.6149   $192.61   $192.60   $192.60  
  Purchase #7 $60.70   10.259%   $66.9272   $66.93   $66.95   $66.90  
  7 purchase totals = $928.40       $1,011.7031   $1,011.70   $1,011.70   $1,011.50