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	$36.91	4.522%	$38.5791	$38.58	$38.60	$38.60
Purchase #2	$229.44	4.535%	$239.8451	$239.85	$239.85	$239.80
Purchase #3	$51.57	6.773%	$55.0628	$55.06	$55.05	$55.10
Purchase #4	$85.81	3.110%	$88.4787	$88.48	$88.50	$88.50
Purchase #5	$212.83	4.366%	$222.1222	$222.12	$222.10	$222.10
Purchase #6	$61.57	5.434%	$64.9157	$64.92	$64.90	$64.90
Purchase #7	$134.48	5.507%	$141.8858	$141.89	$141.90	$141.90
7 purchase totals =	$812.61		$850.8894	$850.90	$850.90	$850.90