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	$109.86	6.500%	$117.0009	$117.00	$117.00	$117.00
Purchase #2	$78.25	6.404%	$83.2611	$83.26	$83.25	$83.30
Purchase #3	$243.54	5.498%	$256.9298	$256.93	$256.95	$256.90
Purchase #4	$30.51	8.419%	$33.0786	$33.08	$33.10	$33.10
Purchase #5	$110.29	7.575%	$118.6445	$118.64	$118.65	$118.60
Purchase #6	$9.79	7.822%	$10.5558	$10.56	$10.55	$10.60
Purchase #7	$37.99	13.423%	$43.0894	$43.09	$43.10	$43.10
7 purchase totals =	$620.23		$662.5601	$662.56	$662.60	$662.60