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	$11.27	10.571%	$12.4614	$12.46	$12.45	$12.50
Purchase #2	$175.56	12.118%	$196.8344	$196.83	$196.85	$196.80
Purchase #3	$52.60	13.751%	$59.833	$59.83	$59.85	$59.80
Purchase #4	$168.82	9.156%	$184.2772	$184.28	$184.30	$184.30
Purchase #5	$29.59	10.240%	$32.62	$32.62	$32.60	$32.60
Purchase #6	$228.84	4.453%	$239.0302	$239.03	$239.05	$239.00
Purchase #7	$143.56	4.732%	$150.3533	$150.35	$150.35	$150.40
7 purchase totals =	$810.24		$875.4095	$875.40	$875.45	$875.40