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	$236.81	5.748%	$250.4218	$250.42	$250.40	$250.40
Purchase #2	$138.75	9.749%	$152.2767	$152.28	$152.30	$152.30
Purchase #3	$91.73	4.478%	$95.8377	$95.84	$95.85	$95.80
Purchase #4	$82.35	9.663%	$90.3075	$90.31	$90.30	$90.30
Purchase #5	$242.65	11.656%	$270.9333	$270.93	$270.95	$270.90
Purchase #6	$59.25	4.469%	$61.8979	$61.90	$61.90	$61.90
Purchase #7	$18.49	12.762%	$20.8497	$20.85	$20.85	$20.80
7 purchase totals =	$870.03		$942.5246	$942.53	$942.55	$942.40