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	$79.66	11.142%	$88.5357	$88.54	$88.55	$88.50
Purchase #2	$145.94	3.343%	$150.8188	$150.82	$150.80	$150.80
Purchase #3	$17.39	8.125%	$18.8029	$18.80	$18.80	$18.80
Purchase #4	$127.83	13.476%	$145.0564	$145.06	$145.05	$145.10
Purchase #5	$199.37	4.842%	$209.0235	$209.02	$209.00	$209.00
Purchase #6	$89.51	12.818%	$100.9834	$100.98	$101.00	$101.00
Purchase #7	$44.82	11.362%	$49.9124	$49.91	$49.90	$49.90
7 purchase totals =	$704.52		$763.1331	$763.13	$763.10	$763.10