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	$84.77	6.364%	$90.1648	$90.16	$90.15	$90.20
Purchase #2	$229.45	8.484%	$248.9165	$248.92	$248.90	$248.90
Purchase #3	$55.74	6.494%	$59.3598	$59.36	$59.35	$59.40
Purchase #4	$131.64	10.596%	$145.5886	$145.59	$145.60	$145.60
Purchase #5	$19.29	5.117%	$20.2771	$20.28	$20.30	$20.30
Purchase #6	$225.73	11.120%	$250.8312	$250.83	$250.85	$250.80
Purchase #7	$122.96	3.246%	$126.9513	$126.95	$126.95	$127.00
7 purchase totals =	$869.58		$942.0893	$942.09	$942.10	$942.20