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	$246.94	6.694%	$263.4702	$263.47	$263.45	$263.50
Purchase #2	$142.25	8.402%	$154.2018	$154.20	$154.20	$154.20
Purchase #3	$215.73	3.665%	$223.6365	$223.64	$223.65	$223.60
Purchase #4	$67.75	11.331%	$75.4268	$75.43	$75.45	$75.40
Purchase #5	$159.60	5.348%	$168.1354	$168.14	$168.15	$168.10
Purchase #6	$116.50	10.115%	$128.284	$128.28	$128.30	$128.30
Purchase #7	$53.46	11.698%	$59.7138	$59.71	$59.70	$59.70
7 purchase totals =	$1,002.23		$1,072.8685	$1,072.87	$1,072.90	$1,072.80