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	$44.78	11.268%	$49.8258	$49.83	$49.85	$49.80
Purchase #2	$130.88	7.320%	$140.4604	$140.46	$140.45	$140.50
Purchase #3	$195.31	9.841%	$214.5305	$214.53	$214.55	$214.50
Purchase #4	$172.93	9.107%	$188.6787	$188.68	$188.70	$188.70
Purchase #5	$198.29	3.614%	$205.4562	$205.46	$205.45	$205.50
Purchase #6	$92.90	7.532%	$99.8972	$99.90	$99.90	$99.90
Purchase #7	$84.89	11.467%	$94.6243	$94.62	$94.60	$94.60
7 purchase totals =	$919.98		$993.4731	$993.48	$993.50	$993.50