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	$134.73	6.600%	$143.6222	$143.62	$143.60	$143.60
Purchase #2	$140.75	3.134%	$145.1611	$145.16	$145.15	$145.20
Purchase #3	$89.85	12.461%	$101.0462	$101.05	$101.05	$101.00
Purchase #4	$112.71	13.478%	$127.9011	$127.90	$127.90	$127.90
Purchase #5	$17.67	7.507%	$18.9965	$19.00	$19.00	$19.00
Purchase #6	$70.53	10.772%	$78.1275	$78.13	$78.15	$78.10
Purchase #7	$20.59	11.273%	$22.9111	$22.91	$22.90	$22.90
7 purchase totals =	$586.83		$637.7657	$637.77	$637.75	$637.70