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 $95.66   6.509%   $101.8865   $101.89   $101.90   $101.90  
  Purchase #2 $192.87   11.304%   $214.672   $214.67   $214.65   $214.70  
  Purchase #3 $244.86   10.465%   $270.4846   $270.48   $270.50   $270.50  
  Purchase #4 $51.54   13.844%   $58.6752   $58.68   $58.70   $58.70  
  Purchase #5 $170.69   3.306%   $176.333   $176.33   $176.35   $176.30  
  Purchase #6 $88.43   3.513%   $91.5365   $91.54   $91.55   $91.50  
  Purchase #7 $136.94   11.336%   $152.4635   $152.46   $152.45   $152.50  
  7 purchase totals = $980.99       $1,066.0513   $1,066.05   $1,066.10   $1,066.10