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	$93.78	5.341%	$98.7888	$98.79	$98.80	$98.80
Purchase #2	$19.35	8.440%	$20.9831	$20.98	$21.00	$21.00
Purchase #3	$147.51	12.463%	$165.8942	$165.89	$165.90	$165.90
Purchase #4	$167.95	4.326%	$175.2155	$175.22	$175.20	$175.20
Purchase #5	$12.44	3.636%	$12.8923	$12.89	$12.90	$12.90
Purchase #6	$35.49	13.493%	$40.2787	$40.28	$40.30	$40.30
Purchase #7	$50.40	5.812%	$53.3292	$53.33	$53.35	$53.30
7 purchase totals =	$526.92		$567.3818	$567.38	$567.45	$567.40