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	$62.37	10.780%	$69.0935	$69.09	$69.10	$69.10
Purchase #2	$144.49	10.465%	$159.6109	$159.61	$159.60	$159.60
Purchase #3	$250.55	5.436%	$264.1699	$264.17	$264.15	$264.20
Purchase #4	$91.87	8.403%	$99.5898	$99.59	$99.60	$99.60
Purchase #5	$129.70	5.539%	$136.8841	$136.88	$136.90	$136.90
Purchase #6	$157.58	13.501%	$178.8549	$178.85	$178.85	$178.90
Purchase #7	$166.33	8.728%	$180.8473	$180.85	$180.85	$180.80
7 purchase totals =	$1,002.89		$1,089.0504	$1,089.04	$1,089.05	$1,089.10