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	$240.53	13.662%	$273.3912	$273.39	$273.40	$273.40
Purchase #2	$179.52	11.871%	$200.8308	$200.83	$200.85	$200.80
Purchase #3	$173.77	5.254%	$182.8999	$182.90	$182.90	$182.90
Purchase #4	$77.59	4.866%	$81.3655	$81.37	$81.35	$81.40
Purchase #5	$208.39	12.440%	$234.3137	$234.31	$234.30	$234.30
Purchase #6	$66.57	7.263%	$71.405	$71.41	$71.40	$71.40
Purchase #7	$67.76	5.694%	$71.6183	$71.62	$71.60	$71.60
7 purchase totals =	$1,014.13		$1,115.8244	$1,115.83	$1,115.80	$1,115.80