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	$205.83	8.623%	$223.5787	$223.58	$223.60	$223.60
Purchase #2	$170.46	7.278%	$182.8661	$182.87	$182.85	$182.90
Purchase #3	$143.85	4.525%	$150.3592	$150.36	$150.35	$150.40
Purchase #4	$143.32	10.251%	$158.0117	$158.01	$158.00	$158.00
Purchase #5	$97.57	3.218%	$100.7098	$100.71	$100.70	$100.70
Purchase #6	$65.76	6.240%	$69.8634	$69.86	$69.85	$69.90
Purchase #7	$108.86	8.590%	$118.2111	$118.21	$118.20	$118.20
7 purchase totals =	$935.65		$1,003.6000	$1,003.60	$1,003.55	$1,003.70