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	$139.82	9.745%	$153.4455	$153.45	$153.45	$153.40
Purchase #2	$130.40	8.496%	$141.4788	$141.48	$141.50	$141.50
Purchase #3	$81.25	12.316%	$91.2568	$91.26	$91.25	$91.30
Purchase #4	$71.57	11.565%	$79.8471	$79.85	$79.85	$79.80
Purchase #5	$105.34	4.454%	$110.0318	$110.03	$110.05	$110.00
Purchase #6	$93.95	7.333%	$100.8394	$100.84	$100.85	$100.80
Purchase #7	$143.72	11.691%	$160.5223	$160.52	$160.50	$160.50
7 purchase totals =	$766.05		$837.4217	$837.43	$837.45	$837.30