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	$81.52	8.271%	$88.2625	$88.26	$88.25	$88.30
Purchase #2	$173.31	13.335%	$196.4209	$196.42	$196.40	$196.40
Purchase #3	$96.82	13.567%	$109.9556	$109.96	$109.95	$110.00
Purchase #4	$136.25	4.768%	$142.7464	$142.75	$142.75	$142.70
Purchase #5	$66.56	10.493%	$73.5441	$73.54	$73.55	$73.50
Purchase #6	$132.54	6.633%	$141.3314	$141.33	$141.35	$141.30
Purchase #7	$159.44	8.216%	$172.5396	$172.54	$172.55	$172.50
7 purchase totals =	$846.44		$924.8005	$924.80	$924.80	$924.70