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	$226.29	11.327%	$251.9219	$251.92	$251.90	$251.90
Purchase #2	$87.74	3.456%	$90.7723	$90.77	$90.75	$90.80
Purchase #3	$220.92	12.502%	$248.5394	$248.54	$248.55	$248.50
Purchase #4	$223.50	3.590%	$231.5237	$231.52	$231.50	$231.50
Purchase #5	$73.37	13.362%	$83.1737	$83.17	$83.15	$83.20
Purchase #6	$33.59	10.236%	$37.0283	$37.03	$37.05	$37.00
Purchase #7	$250.82	6.811%	$267.9034	$267.90	$267.90	$267.90
7 purchase totals =	$1,116.23		$1,210.8627	$1,210.85	$1,210.80	$1,210.80