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	$208.94	6.712%	$222.9641	$222.96	$222.95	$223.00
Purchase #2	$158.96	9.288%	$173.7242	$173.72	$173.70	$173.70
Purchase #3	$235.40	5.505%	$248.3588	$248.36	$248.35	$248.40
Purchase #4	$140.33	8.596%	$152.3928	$152.39	$152.40	$152.40
Purchase #5	$100.99	10.391%	$111.4839	$111.48	$111.50	$111.50
Purchase #6	$239.81	11.815%	$268.1436	$268.14	$268.15	$268.10
Purchase #7	$81.45	9.216%	$88.9564	$88.96	$88.95	$89.00
7 purchase totals =	$1,165.88		$1,266.0238	$1,266.01	$1,266.00	$1,266.10