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	$79.50	13.802%	$90.4726	$90.47	$90.45	$90.50
Purchase #2	$117.55	10.349%	$129.7152	$129.72	$129.70	$129.70
Purchase #3	$168.34	12.102%	$188.7125	$188.71	$188.70	$188.70
Purchase #4	$181.27	4.241%	$188.9577	$188.96	$188.95	$189.00
Purchase #5	$227.34	11.757%	$254.0684	$254.07	$254.05	$254.10
Purchase #6	$193.58	13.672%	$220.0463	$220.05	$220.05	$220.00
Purchase #7	$104.89	8.293%	$113.5885	$113.59	$113.60	$113.60
7 purchase totals =	$1,072.47		$1,185.5612	$1,185.57	$1,185.50	$1,185.60