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	$225.89	12.174%	$253.3898	$253.39	$253.40	$253.40
Purchase #2	$44.35	5.790%	$46.9179	$46.92	$46.90	$46.90
Purchase #3	$100.98	10.224%	$111.3042	$111.30	$111.30	$111.30
Purchase #4	$56.71	7.215%	$60.8016	$60.80	$60.80	$60.80
Purchase #5	$105.82	3.411%	$109.4295	$109.43	$109.45	$109.40
Purchase #6	$129.53	13.611%	$147.1603	$147.16	$147.15	$147.20
Purchase #7	$101.44	7.688%	$109.2387	$109.24	$109.25	$109.20
7 purchase totals =	$764.72		$838.2420	$838.24	$838.25	$838.20