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	$52.84	8.127%	$57.1343	$57.13	$57.15	$57.10
Purchase #2	$146.30	5.426%	$154.2382	$154.24	$154.25	$154.20
Purchase #3	$102.84	6.667%	$109.6963	$109.70	$109.70	$109.70
Purchase #4	$49.56	5.644%	$52.3572	$52.36	$52.35	$52.40
Purchase #5	$76.34	3.142%	$78.7386	$78.74	$78.75	$78.70
Purchase #6	$18.43	10.269%	$20.3226	$20.32	$20.30	$20.30
Purchase #7	$78.49	8.690%	$85.3108	$85.31	$85.30	$85.30
7 purchase totals =	$524.80		$557.7980	$557.80	$557.80	$557.70