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 $60.83   11.844%   $68.0347   $68.03   $68.05   $68.00  
  Purchase #2 $38.78   13.111%   $43.8644   $43.86   $43.85   $43.90  
  Purchase #3 $223.62   13.307%   $253.3771   $253.38   $253.40   $253.40  
  Purchase #4 $167.26   11.789%   $186.9783   $186.98   $187.00   $187.00  
  Purchase #5 $163.55   13.804%   $186.1264   $186.13   $186.15   $186.10  
  Purchase #6 $194.56   7.541%   $209.2318   $209.23   $209.25   $209.20  
  Purchase #7 $225.53   8.764%   $245.2954   $245.30   $245.30   $245.30  
  7 purchase totals = $1,074.13       $1,192.9081   $1,192.91   $1,193.00   $1,192.90