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	$73.84	7.800%	$79.5995	$79.60	$79.60	$79.60
Purchase #2	$37.92	7.823%	$40.8865	$40.89	$40.90	$40.90
Purchase #3	$191.83	10.356%	$211.6959	$211.70	$211.70	$211.70
Purchase #4	$183.81	9.158%	$200.6433	$200.64	$200.65	$200.60
Purchase #5	$165.96	6.355%	$176.5068	$176.51	$176.50	$176.50
Purchase #6	$27.99	12.599%	$31.5165	$31.52	$31.50	$31.50
Purchase #7	$169.89	13.174%	$192.2713	$192.27	$192.25	$192.30
7 purchase totals =	$851.24		$933.1198	$933.13	$933.10	$933.10