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	$54.70	3.142%	$56.4187	$56.42	$56.40	$56.40
Purchase #2	$179.69	4.797%	$188.3097	$188.31	$188.30	$188.30
Purchase #3	$37.91	7.203%	$40.6407	$40.64	$40.65	$40.60
Purchase #4	$38.25	8.873%	$41.6439	$41.64	$41.65	$41.60
Purchase #5	$175.81	8.621%	$190.9666	$190.97	$190.95	$191.00
Purchase #6	$167.51	10.833%	$185.6564	$185.66	$185.65	$185.70
Purchase #7	$65.71	3.313%	$67.887	$67.89	$67.90	$67.90
7 purchase totals =	$719.58		$771.5230	$771.53	$771.50	$771.50