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	$35.61	9.814%	$39.1048	$39.10	$39.10	$39.10
Purchase #2	$84.64	9.492%	$92.674	$92.67	$92.65	$92.70
Purchase #3	$105.96	7.760%	$114.1825	$114.18	$114.20	$114.20
Purchase #4	$39.79	13.747%	$45.2599	$45.26	$45.25	$45.30
Purchase #5	$146.71	3.547%	$151.9138	$151.91	$151.90	$151.90
Purchase #6	$79.44	13.200%	$89.9261	$89.93	$89.95	$89.90
Purchase #7	$119.32	6.707%	$127.3228	$127.32	$127.30	$127.30
7 purchase totals =	$611.47		$660.3839	$660.37	$660.35	$660.40