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	$19.34	3.530%	$20.0227	$20.02	$20.00	$20.00
Purchase #2	$145.39	4.462%	$151.8773	$151.88	$151.90	$151.90
Purchase #3	$200.94	11.247%	$223.5397	$223.54	$223.55	$223.50
Purchase #4	$207.87	6.819%	$222.0447	$222.04	$222.05	$222.00
Purchase #5	$6.91	11.278%	$7.6893	$7.69	$7.70	$7.70
Purchase #6	$216.43	3.319%	$223.6133	$223.61	$223.60	$223.60
Purchase #7	$181.51	4.628%	$189.9103	$189.91	$189.90	$189.90
7 purchase totals =	$978.39		$1,038.6973	$1,038.69	$1,038.70	$1,038.60