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 $55.99   11.264%   $62.2967   $62.30   $62.30   $62.30  
  Purchase #2 $223.31   13.403%   $253.2402   $253.24   $253.25   $253.20  
  Purchase #3 $230.68   12.519%   $259.5588   $259.56   $259.55   $259.60  
  Purchase #4 $159.30   10.689%   $176.3276   $176.33   $176.35   $176.30  
  Purchase #5 $57.86   13.428%   $65.6294   $65.63   $65.65   $65.60  
  Purchase #6 $201.88   12.567%   $227.2503   $227.25   $227.25   $227.30  
  Purchase #7 $241.63   4.305%   $252.0322   $252.03   $252.05   $252.00  
  7 purchase totals = $1,170.65       $1,296.3352   $1,296.34   $1,296.40   $1,296.30