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	$56.69	8.391%	$61.4469	$61.45	$61.45	$61.40
Purchase #2	$32.35	12.155%	$36.2821	$36.28	$36.30	$36.30
Purchase #3	$91.56	10.753%	$101.4054	$101.41	$101.40	$101.40
Purchase #4	$79.25	13.174%	$89.6904	$89.69	$89.70	$89.70
Purchase #5	$6.37	6.611%	$6.7911	$6.79	$6.80	$6.80
Purchase #6	$141.54	7.323%	$151.905	$151.91	$151.90	$151.90
Purchase #7	$121.71	10.219%	$134.1475	$134.15	$134.15	$134.10
7 purchase totals =	$529.47		$581.6684	$581.68	$581.70	$581.60