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	$227.52	8.641%	$247.18	$247.18	$247.20	$247.20
Purchase #2	$90.59	10.116%	$99.7541	$99.75	$99.75	$99.80
Purchase #3	$112.26	11.202%	$124.8354	$124.84	$124.85	$124.80
Purchase #4	$74.63	7.438%	$80.181	$80.18	$80.20	$80.20
Purchase #5	$50.27	6.337%	$53.4556	$53.46	$53.45	$53.50
Purchase #6	$165.50	8.669%	$179.8472	$179.85	$179.85	$179.80
Purchase #7	$59.92	12.303%	$67.292	$67.29	$67.30	$67.30
7 purchase totals =	$780.69		$852.5453	$852.55	$852.60	$852.60