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	$83.28	7.609%	$89.6168	$89.62	$89.60	$89.60
Purchase #2	$53.49	11.514%	$59.6488	$59.65	$59.65	$59.60
Purchase #3	$94.30	11.460%	$105.1068	$105.11	$105.10	$105.10
Purchase #4	$27.98	3.209%	$28.8779	$28.88	$28.90	$28.90
Purchase #5	$141.84	12.782%	$159.97	$159.97	$159.95	$160.00
Purchase #6	$179.61	5.107%	$188.7827	$188.78	$188.80	$188.80
Purchase #7	$246.45	5.825%	$260.8057	$260.81	$260.80	$260.80
7 purchase totals =	$826.95		$892.8087	$892.82	$892.80	$892.80