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 $68.97   9.647%   $75.6235   $75.62   $75.60   $75.60  
  Purchase #2 $237.56   7.474%   $255.3152   $255.32   $255.30   $255.30  
  Purchase #3 $203.94   3.238%   $210.5436   $210.54   $210.55   $210.50  
  Purchase #4 $91.41   5.509%   $96.4458   $96.45   $96.45   $96.40  
  Purchase #5 $79.64   10.631%   $88.1065   $88.11   $88.10   $88.10  
  Purchase #6 $177.40   4.522%   $185.422   $185.42   $185.40   $185.40  
  Purchase #7 $151.55   5.439%   $159.7928   $159.79   $159.80   $159.80  
  7 purchase totals = $1,010.47       $1,071.2494   $1,071.25   $1,071.20   $1,071.10