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	$160.82	6.148%	$170.7072	$170.71	$170.70	$170.70
Purchase #2	$124.32	5.477%	$131.129	$131.13	$131.15	$131.10
Purchase #3	$101.83	9.503%	$111.5069	$111.51	$111.50	$111.50
Purchase #4	$110.54	4.137%	$115.113	$115.11	$115.10	$115.10
Purchase #5	$236.49	3.826%	$245.5381	$245.54	$245.55	$245.50
Purchase #6	$78.40	12.412%	$88.131	$88.13	$88.15	$88.10
Purchase #7	$68.78	10.713%	$76.1484	$76.15	$76.15	$76.10
7 purchase totals =	$881.18		$938.2736	$938.28	$938.30	$938.10