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	$120.57	7.629%	$129.7683	$129.77	$129.75	$129.80
Purchase #2	$79.94	11.363%	$89.0236	$89.02	$89.00	$89.00
Purchase #3	$122.71	3.715%	$127.2687	$127.27	$127.25	$127.30
Purchase #4	$197.34	8.706%	$214.5204	$214.52	$214.50	$214.50
Purchase #5	$213.91	7.296%	$229.5169	$229.52	$229.50	$229.50
Purchase #6	$80.78	3.541%	$83.6404	$83.64	$83.65	$83.60
Purchase #7	$43.66	3.472%	$45.1759	$45.18	$45.20	$45.20
7 purchase totals =	$858.91		$918.9142	$918.92	$918.85	$918.90