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	$46.27	12.179%	$51.9052	$51.91	$51.90	$51.90
Purchase #2	$73.96	8.872%	$80.5217	$80.52	$80.50	$80.50
Purchase #3	$70.98	12.568%	$79.9008	$79.90	$79.90	$79.90
Purchase #4	$96.25	4.727%	$100.7997	$100.80	$100.80	$100.80
Purchase #5	$46.75	7.756%	$50.3759	$50.38	$50.40	$50.40
Purchase #6	$191.66	8.123%	$207.2285	$207.23	$207.25	$207.20
Purchase #7	$48.91	10.228%	$53.9125	$53.91	$53.90	$53.90
7 purchase totals =	$574.78		$624.6443	$624.65	$624.65	$624.60