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	$52.84	4.846%	$55.4006	$55.40	$55.40	$55.40
Purchase #2	$164.53	13.712%	$187.0904	$187.09	$187.10	$187.10
Purchase #3	$129.45	10.105%	$142.5309	$142.53	$142.55	$142.50
Purchase #4	$24.88	5.713%	$26.3014	$26.30	$26.30	$26.30
Purchase #5	$158.79	8.614%	$172.4682	$172.47	$172.45	$172.50
Purchase #6	$234.55	8.434%	$254.3319	$254.33	$254.35	$254.30
Purchase #7	$136.85	3.699%	$141.9121	$141.91	$141.90	$141.90
7 purchase totals =	$901.89		$980.0355	$980.03	$980.05	$980.00