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	$101.98	8.205%	$110.3475	$110.35	$110.35	$110.30
Purchase #2	$96.54	9.298%	$105.5163	$105.52	$105.50	$105.50
Purchase #3	$37.80	10.738%	$41.859	$41.86	$41.85	$41.90
Purchase #4	$119.28	6.649%	$127.2109	$127.21	$127.20	$127.20
Purchase #5	$81.98	10.703%	$90.7543	$90.75	$90.75	$90.80
Purchase #6	$170.41	12.519%	$191.7436	$191.74	$191.75	$191.70
Purchase #7	$12.66	9.455%	$13.857	$13.86	$13.85	$13.90
7 purchase totals =	$620.65		$681.2886	$681.29	$681.25	$681.30