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 $91.90   4.762%   $96.2763   $96.28   $96.30   $96.30  
  Purchase #2 $169.25   9.437%   $185.2221   $185.22   $185.20   $185.20  
  Purchase #3 $180.91   11.857%   $202.3605   $202.36   $202.35   $202.40  
  Purchase #4 $166.39   12.211%   $186.7079   $186.71   $186.70   $186.70  
  Purchase #5 $51.55   3.786%   $53.5017   $53.50   $53.50   $53.50  
  Purchase #6 $136.72   8.658%   $148.5572   $148.56   $148.55   $148.60  
  Purchase #7 $186.98   11.511%   $208.5033   $208.50   $208.50   $208.50  
  7 purchase totals = $983.70       $1,081.1290   $1,081.13   $1,081.10   $1,081.20