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	$96.79	4.225%	$100.8794	$100.88	$100.90	$100.90
Purchase #2	$140.58	3.729%	$145.8222	$145.82	$145.80	$145.80
Purchase #3	$59.94	11.183%	$66.6431	$66.64	$66.65	$66.60
Purchase #4	$159.56	12.639%	$179.7268	$179.73	$179.75	$179.70
Purchase #5	$118.34	10.841%	$131.1692	$131.17	$131.15	$131.20
Purchase #6	$155.64	4.471%	$162.5987	$162.60	$162.60	$162.60
Purchase #7	$141.98	3.613%	$147.1097	$147.11	$147.10	$147.10
7 purchase totals =	$872.83		$933.9491	$933.95	$933.95	$933.90