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	$244.80	3.828%	$254.1709	$254.17	$254.15	$254.20
Purchase #2	$200.66	13.815%	$228.3812	$228.38	$228.40	$228.40
Purchase #3	$46.46	13.387%	$52.6796	$52.68	$52.70	$52.70
Purchase #4	$88.66	11.578%	$98.9251	$98.93	$98.95	$98.90
Purchase #5	$135.37	7.325%	$145.2859	$145.29	$145.30	$145.30
Purchase #6	$30.86	7.287%	$33.1088	$33.11	$33.10	$33.10
Purchase #7	$148.70	11.643%	$166.0131	$166.01	$166.00	$166.00
7 purchase totals =	$895.51		$978.5646	$978.57	$978.60	$978.60