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	$98.72	4.231%	$102.8968	$102.90	$102.90	$102.90
Purchase #2	$123.65	3.406%	$127.8615	$127.86	$127.85	$127.90
Purchase #3	$210.94	8.608%	$229.0977	$229.10	$229.10	$229.10
Purchase #4	$88.29	6.434%	$93.9706	$93.97	$93.95	$94.00
Purchase #5	$128.89	6.420%	$137.1647	$137.16	$137.15	$137.20
Purchase #6	$168.58	12.541%	$189.7216	$189.72	$189.70	$189.70
Purchase #7	$98.59	11.306%	$109.7366	$109.74	$109.75	$109.70
7 purchase totals =	$917.66		$990.4495	$990.45	$990.40	$990.50