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 $56.89   6.229%   $60.4337   $60.43   $60.45   $60.40  
  Purchase #2 $128.85   11.509%   $143.6793   $143.68   $143.70   $143.70  
  Purchase #3 $56.37   3.603%   $58.401   $58.40   $58.40   $58.40  
  Purchase #4 $214.79   12.644%   $241.948   $241.95   $241.95   $241.90  
  Purchase #5 $53.64   7.385%   $57.6013   $57.60   $57.60   $57.60  
  Purchase #6 $87.62   13.516%   $99.4627   $99.46   $99.45   $99.50  
  Purchase #7 $87.67   6.772%   $93.607   $93.61   $93.60   $93.60  
  7 purchase totals = $685.83       $755.1330   $755.13   $755.15   $755.10