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	$110.81	9.581%	$121.4267	$121.43	$121.45	$121.40
Purchase #2	$96.83	13.512%	$109.9137	$109.91	$109.90	$109.90
Purchase #3	$234.45	7.508%	$252.0525	$252.05	$252.05	$252.10
Purchase #4	$244.55	4.114%	$254.6108	$254.61	$254.60	$254.60
Purchase #5	$137.32	12.610%	$154.6361	$154.64	$154.65	$154.60
Purchase #6	$70.95	9.775%	$77.8854	$77.89	$77.90	$77.90
Purchase #7	$83.30	9.666%	$91.3518	$91.35	$91.35	$91.40
7 purchase totals =	$978.21		$1,061.8770	$1,061.88	$1,061.90	$1,061.90