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	$172.45	3.854%	$179.0962	$179.10	$179.10	$179.10
Purchase #2	$61.55	9.580%	$67.4465	$67.45	$67.45	$67.40
Purchase #3	$103.76	5.643%	$109.6152	$109.62	$109.60	$109.60
Purchase #4	$103.85	10.672%	$114.9329	$114.93	$114.95	$114.90
Purchase #5	$36.41	12.297%	$40.8873	$40.89	$40.90	$40.90
Purchase #6	$138.98	11.201%	$154.5471	$154.55	$154.55	$154.50
Purchase #7	$202.50	11.785%	$226.3646	$226.36	$226.35	$226.40
7 purchase totals =	$819.50		$892.8898	$892.90	$892.90	$892.80