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	$249.96	6.551%	$266.3349	$266.33	$266.35	$266.30
Purchase #2	$101.54	4.720%	$106.3327	$106.33	$106.35	$106.30
Purchase #3	$95.76	4.555%	$100.1219	$100.12	$100.10	$100.10
Purchase #4	$208.32	7.131%	$223.1753	$223.18	$223.20	$223.20
Purchase #5	$139.40	10.820%	$154.4831	$154.48	$154.50	$154.50
Purchase #6	$70.88	13.324%	$80.3241	$80.32	$80.30	$80.30
Purchase #7	$156.35	8.256%	$169.2583	$169.26	$169.25	$169.30
7 purchase totals =	$1,022.21		$1,100.0303	$1,100.02	$1,100.05	$1,100.00