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	$244.97	10.407%	$270.464	$270.46	$270.45	$270.50
Purchase #2	$227.83	11.515%	$254.0646	$254.06	$254.05	$254.10
Purchase #3	$123.55	12.529%	$139.0296	$139.03	$139.05	$139.00
Purchase #4	$141.76	13.472%	$160.8579	$160.86	$160.85	$160.90
Purchase #5	$192.72	9.203%	$210.456	$210.46	$210.45	$210.50
Purchase #6	$227.58	12.536%	$256.1094	$256.11	$256.10	$256.10
Purchase #7	$108.76	10.648%	$120.3408	$120.34	$120.35	$120.30
7 purchase totals =	$1,267.17		$1,411.3223	$1,411.32	$1,411.30	$1,411.40