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	$36.67	10.448%	$40.5013	$40.50	$40.50	$40.50
Purchase #2	$211.40	12.179%	$237.1464	$237.15	$237.15	$237.10
Purchase #3	$121.61	4.864%	$127.5251	$127.53	$127.55	$127.50
Purchase #4	$217.69	8.501%	$236.1958	$236.20	$236.20	$236.20
Purchase #5	$151.92	10.368%	$167.6711	$167.67	$167.65	$167.70
Purchase #6	$61.30	5.210%	$64.4937	$64.49	$64.50	$64.50
Purchase #7	$115.93	11.222%	$128.9397	$128.94	$128.95	$128.90
7 purchase totals =	$916.52		$1,002.4731	$1,002.48	$1,002.50	$1,002.40