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	$69.27	12.850%	$78.1712	$78.17	$78.15	$78.20
Purchase #2	$111.52	5.191%	$117.309	$117.31	$117.30	$117.30
Purchase #3	$82.63	11.180%	$91.868	$91.87	$91.85	$91.90
Purchase #4	$165.45	4.428%	$172.7761	$172.78	$172.80	$172.80
Purchase #5	$48.50	10.617%	$53.6492	$53.65	$53.65	$53.60
Purchase #6	$89.56	13.380%	$101.5431	$101.54	$101.55	$101.50
Purchase #7	$53.51	13.833%	$60.912	$60.91	$60.90	$60.90
7 purchase totals =	$620.44		$676.2286	$676.23	$676.20	$676.20