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	$131.65	4.167%	$137.1359	$137.14	$137.15	$137.10
Purchase #2	$127.62	8.506%	$138.4754	$138.48	$138.50	$138.50
Purchase #3	$208.66	6.514%	$222.2521	$222.25	$222.25	$222.30
Purchase #4	$37.48	13.270%	$42.4536	$42.45	$42.45	$42.50
Purchase #5	$153.40	7.380%	$164.7209	$164.72	$164.70	$164.70
Purchase #6	$188.27	9.830%	$206.7769	$206.78	$206.80	$206.80
Purchase #7	$110.31	12.798%	$124.4275	$124.43	$124.45	$124.40
7 purchase totals =	$957.39		$1,036.2423	$1,036.25	$1,036.30	$1,036.30