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	$48.61	12.158%	$54.52	$54.52	$54.50	$54.50
Purchase #2	$123.44	6.301%	$131.218	$131.22	$131.20	$131.20
Purchase #3	$130.48	4.479%	$136.3242	$136.32	$136.30	$136.30
Purchase #4	$169.63	11.468%	$189.0832	$189.08	$189.10	$189.10
Purchase #5	$198.80	13.491%	$225.6201	$225.62	$225.60	$225.60
Purchase #6	$169.88	6.283%	$180.5536	$180.55	$180.55	$180.60
Purchase #7	$111.34	11.413%	$124.0472	$124.05	$124.05	$124.00
7 purchase totals =	$952.18		$1,041.3663	$1,041.36	$1,041.30	$1,041.30