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	$30.61	5.745%	$32.3685	$32.37	$32.35	$32.40
Purchase #2	$53.82	10.229%	$59.3252	$59.33	$59.35	$59.30
Purchase #3	$105.60	11.861%	$118.1252	$118.13	$118.15	$118.10
Purchase #4	$176.97	7.469%	$190.1879	$190.19	$190.20	$190.20
Purchase #5	$68.40	4.805%	$71.6866	$71.69	$71.70	$71.70
Purchase #6	$57.75	12.549%	$64.997	$65.00	$65.00	$65.00
Purchase #7	$249.38	7.168%	$267.2556	$267.26	$267.25	$267.30
7 purchase totals =	$742.53		$803.9460	$803.97	$804.00	$804.00