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	$180.75	6.495%	$192.4897	$192.49	$192.50	$192.50
Purchase #2	$99.71	7.200%	$106.8891	$106.89	$106.90	$106.90
Purchase #3	$19.45	9.274%	$21.2538	$21.25	$21.25	$21.30
Purchase #4	$45.31	8.640%	$49.2248	$49.22	$49.20	$49.20
Purchase #5	$83.79	6.614%	$89.3319	$89.33	$89.35	$89.30
Purchase #6	$217.64	7.145%	$233.1904	$233.19	$233.20	$233.20
Purchase #7	$139.64	12.116%	$156.5588	$156.56	$156.55	$156.60
7 purchase totals =	$786.29		$848.9385	$848.93	$848.95	$849.00