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	$235.94	6.671%	$251.6796	$251.68	$251.70	$251.70
Purchase #2	$232.39	9.390%	$254.2114	$254.21	$254.20	$254.20
Purchase #3	$122.77	9.277%	$134.1594	$134.16	$134.15	$134.20
Purchase #4	$122.63	7.410%	$131.7169	$131.72	$131.70	$131.70
Purchase #5	$88.64	12.119%	$99.3823	$99.38	$99.40	$99.40
Purchase #6	$65.62	3.369%	$67.8307	$67.83	$67.85	$67.80
Purchase #7	$160.83	3.231%	$166.0264	$166.03	$166.05	$166.00
7 purchase totals =	$1,028.82		$1,105.0067	$1,105.01	$1,105.05	$1,105.00