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	$186.69	6.859%	$199.4951	$199.50	$199.50	$199.50
Purchase #2	$80.47	10.463%	$88.8896	$88.89	$88.90	$88.90
Purchase #3	$188.62	9.789%	$207.084	$207.08	$207.10	$207.10
Purchase #4	$18.95	8.454%	$20.552	$20.55	$20.55	$20.60
Purchase #5	$155.48	10.332%	$171.5442	$171.54	$171.55	$171.50
Purchase #6	$96.91	9.135%	$105.7627	$105.76	$105.75	$105.80
Purchase #7	$115.52	10.683%	$127.861	$127.86	$127.85	$127.90
7 purchase totals =	$842.64		$921.1886	$921.18	$921.20	$921.30