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 $56.45   3.707%   $58.5426   $58.54   $58.55   $58.50  
  Purchase #2 $215.96   4.660%   $226.0237   $226.02   $226.00   $226.00  
  Purchase #3 $59.65   8.409%   $64.666   $64.67   $64.65   $64.70  
  Purchase #4 $148.45   6.853%   $158.6233   $158.62   $158.60   $158.60  
  Purchase #5 $200.45   5.662%   $211.7995   $211.80   $211.80   $211.80  
  Purchase #6 $76.69   10.473%   $84.7217   $84.72   $84.70   $84.70  
  Purchase #7 $94.63   4.132%   $98.5401   $98.54   $98.55   $98.50  
  7 purchase totals = $852.28       $902.9169   $902.91   $902.85   $902.80