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	$16.82	10.172%	$18.5309	$18.53	$18.55	$18.50
Purchase #2	$60.44	4.449%	$63.129	$63.13	$63.15	$63.10
Purchase #3	$123.90	4.114%	$128.9972	$129.00	$129.00	$129.00
Purchase #4	$59.26	3.508%	$61.3388	$61.34	$61.35	$61.30
Purchase #5	$92.39	4.298%	$96.3609	$96.36	$96.35	$96.40
Purchase #6	$10.86	11.868%	$12.1489	$12.15	$12.15	$12.10
Purchase #7	$18.54	9.546%	$20.3098	$20.31	$20.30	$20.30
7 purchase totals =	$382.21		$400.8155	$400.82	$400.85	$400.70