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	$52.58	6.331%	$55.9088	$55.91	$55.90	$55.90
Purchase #2	$181.98	11.272%	$202.4928	$202.49	$202.50	$202.50
Purchase #3	$170.42	8.785%	$185.3914	$185.39	$185.40	$185.40
Purchase #4	$162.25	10.438%	$179.1857	$179.19	$179.20	$179.20
Purchase #5	$114.87	7.198%	$123.1383	$123.14	$123.15	$123.10
Purchase #6	$234.94	13.280%	$266.14	$266.14	$266.15	$266.10
Purchase #7	$127.98	12.403%	$143.8534	$143.85	$143.85	$143.90
7 purchase totals =	$1,045.02		$1,156.1104	$1,156.11	$1,156.15	$1,156.10