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	$32.98	12.388%	$37.0656	$37.07	$37.05	$37.10
Purchase #2	$66.88	9.286%	$73.0905	$73.09	$73.10	$73.10
Purchase #3	$116.78	12.437%	$131.3039	$131.30	$131.30	$131.30
Purchase #4	$105.25	4.367%	$109.8463	$109.85	$109.85	$109.80
Purchase #5	$93.54	9.447%	$102.3767	$102.38	$102.40	$102.40
Purchase #6	$215.57	10.544%	$238.2997	$238.30	$238.30	$238.30
Purchase #7	$92.75	6.444%	$98.7268	$98.73	$98.75	$98.70
7 purchase totals =	$723.75		$790.7095	$790.72	$790.75	$790.70