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	$247.92	12.207%	$278.1836	$278.18	$278.20	$278.20
Purchase #2	$154.73	8.521%	$167.9145	$167.91	$167.90	$167.90
Purchase #3	$128.59	12.716%	$144.9415	$144.94	$144.95	$144.90
Purchase #4	$132.59	11.841%	$148.29	$148.29	$148.30	$148.30
Purchase #5	$178.80	5.813%	$189.1936	$189.19	$189.20	$189.20
Purchase #6	$33.52	6.168%	$35.5875	$35.59	$35.60	$35.60
Purchase #7	$191.32	9.411%	$209.3251	$209.33	$209.35	$209.30
7 purchase totals =	$1,067.47		$1,173.4358	$1,173.43	$1,173.50	$1,173.40