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 $92.99   5.756%   $98.3425   $98.34   $98.35   $98.30  
  Purchase #2 $75.32   13.661%   $85.6095   $85.61   $85.60   $85.60  
  Purchase #3 $130.54   5.848%   $138.174   $138.17   $138.15   $138.20  
  Purchase #4 $77.76   12.211%   $87.2553   $87.26   $87.25   $87.30  
  Purchase #5 $29.36   9.840%   $32.249   $32.25   $32.25   $32.20  
  Purchase #6 $103.77   4.170%   $108.0972   $108.10   $108.10   $108.10  
  Purchase #7 $184.62   5.412%   $194.6116   $194.61   $194.60   $194.60  
  7 purchase totals = $694.36       $744.3391   $744.34   $744.30   $744.30