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	$34.83	6.455%	$37.0783	$37.08	$37.10	$37.10
Purchase #2	$89.56	10.560%	$99.0175	$99.02	$99.00	$99.00
Purchase #3	$91.47	11.405%	$101.9022	$101.90	$101.90	$101.90
Purchase #4	$154.99	13.367%	$175.7075	$175.71	$175.70	$175.70
Purchase #5	$172.55	9.444%	$188.8456	$188.85	$188.85	$188.80
Purchase #6	$97.49	8.205%	$105.4891	$105.49	$105.50	$105.50
Purchase #7	$118.53	10.732%	$131.2506	$131.25	$131.25	$131.30
7 purchase totals =	$759.42		$839.2908	$839.30	$839.30	$839.30