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	$90.49	10.314%	$99.8231	$99.82	$99.80	$99.80
Purchase #2	$23.58	6.253%	$25.0545	$25.05	$25.05	$25.10
Purchase #3	$36.61	6.772%	$39.0892	$39.09	$39.10	$39.10
Purchase #4	$89.74	9.393%	$98.1693	$98.17	$98.15	$98.20
Purchase #5	$133.59	13.751%	$151.96	$151.96	$151.95	$152.00
Purchase #6	$104.83	8.700%	$113.9502	$113.95	$113.95	$114.00
Purchase #7	$105.39	4.823%	$110.473	$110.47	$110.45	$110.50
7 purchase totals =	$584.23		$638.5193	$638.51	$638.45	$638.70