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	$140.71	4.680%	$147.2952	$147.30	$147.30	$147.30
Purchase #2	$52.49	13.386%	$59.5163	$59.52	$59.50	$59.50
Purchase #3	$197.64	11.337%	$220.0464	$220.05	$220.05	$220.00
Purchase #4	$83.86	7.303%	$89.9843	$89.98	$90.00	$90.00
Purchase #5	$105.35	6.444%	$112.1388	$112.14	$112.15	$112.10
Purchase #6	$206.86	13.754%	$235.3115	$235.31	$235.30	$235.30
Purchase #7	$129.95	10.800%	$143.9846	$143.98	$144.00	$144.00
7 purchase totals =	$916.86		$1,008.2771	$1,008.28	$1,008.30	$1,008.20