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	$227.31	12.325%	$255.326	$255.33	$255.35	$255.30
Purchase #2	$225.47	5.807%	$238.563	$238.56	$238.55	$238.60
Purchase #3	$110.67	4.445%	$115.5893	$115.59	$115.60	$115.60
Purchase #4	$153.29	9.696%	$168.153	$168.15	$168.15	$168.20
Purchase #5	$102.50	3.496%	$106.0834	$106.08	$106.10	$106.10
Purchase #6	$20.33	10.717%	$22.5088	$22.51	$22.50	$22.50
Purchase #7	$123.80	7.467%	$133.0441	$133.04	$133.05	$133.00
7 purchase totals =	$963.37		$1,039.2676	$1,039.26	$1,039.30	$1,039.30