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	$46.26	9.721%	$50.7569	$50.76	$50.75	$50.80
Purchase #2	$77.36	3.761%	$80.2695	$80.27	$80.25	$80.30
Purchase #3	$65.25	10.612%	$72.1743	$72.17	$72.15	$72.20
Purchase #4	$88.63	4.272%	$92.4163	$92.42	$92.40	$92.40
Purchase #5	$6.44	11.404%	$7.1744	$7.17	$7.15	$7.20
Purchase #6	$123.85	6.345%	$131.7083	$131.71	$131.70	$131.70
Purchase #7	$9.71	8.777%	$10.5622	$10.56	$10.55	$10.60
7 purchase totals =	$417.50		$445.0619	$445.06	$444.95	$445.20