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	$17.63	3.623%	$18.2687	$18.27	$18.25	$18.30
Purchase #2	$191.67	13.699%	$217.9269	$217.93	$217.95	$217.90
Purchase #3	$100.81	12.408%	$113.3185	$113.32	$113.30	$113.30
Purchase #4	$118.81	7.594%	$127.8324	$127.83	$127.85	$127.80
Purchase #5	$151.64	13.516%	$172.1357	$172.14	$172.15	$172.10
Purchase #6	$210.74	8.792%	$229.2683	$229.27	$229.25	$229.30
Purchase #7	$89.53	9.326%	$97.8796	$97.88	$97.90	$97.90
7 purchase totals =	$880.83		$976.6301	$976.64	$976.65	$976.60