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	$172.56	4.206%	$179.8179	$179.82	$179.80	$179.80
Purchase #2	$40.84	3.244%	$42.1648	$42.16	$42.15	$42.20
Purchase #3	$139.34	3.519%	$144.2434	$144.24	$144.25	$144.20
Purchase #4	$235.54	12.123%	$264.0945	$264.09	$264.10	$264.10
Purchase #5	$32.81	7.340%	$35.2183	$35.22	$35.20	$35.20
Purchase #6	$137.43	9.373%	$150.3113	$150.31	$150.30	$150.30
Purchase #7	$145.88	6.796%	$155.794	$155.79	$155.80	$155.80
7 purchase totals =	$904.40		$971.6442	$971.63	$971.60	$971.60