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	$101.31	8.779%	$110.204	$110.20	$110.20	$110.20
Purchase #2	$132.66	13.748%	$150.8981	$150.90	$150.90	$150.90
Purchase #3	$98.38	4.828%	$103.1298	$103.13	$103.15	$103.10
Purchase #4	$250.62	7.459%	$269.3137	$269.31	$269.30	$269.30
Purchase #5	$132.91	13.739%	$151.1705	$151.17	$151.15	$151.20
Purchase #6	$228.52	5.427%	$240.9218	$240.92	$240.90	$240.90
Purchase #7	$142.58	8.662%	$154.9303	$154.93	$154.95	$154.90
7 purchase totals =	$1,086.98		$1,180.5682	$1,180.56	$1,180.55	$1,180.50