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	$61.37	7.365%	$65.8899	$65.89	$65.90	$65.90
Purchase #2	$184.84	10.872%	$204.9358	$204.94	$204.95	$204.90
Purchase #3	$126.83	10.536%	$140.1928	$140.19	$140.20	$140.20
Purchase #4	$82.44	9.122%	$89.9602	$89.96	$89.95	$90.00
Purchase #5	$44.89	12.693%	$50.5879	$50.59	$50.60	$50.60
Purchase #6	$62.42	5.201%	$65.6665	$65.67	$65.65	$65.70
Purchase #7	$84.85	11.813%	$94.8733	$94.87	$94.85	$94.90
7 purchase totals =	$647.64		$712.1064	$712.11	$712.10	$712.20