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	$111.68	7.776%	$120.3642	$120.36	$120.35	$120.40
Purchase #2	$13.58	11.527%	$15.1454	$15.15	$15.15	$15.10
Purchase #3	$68.58	5.155%	$72.1153	$72.12	$72.10	$72.10
Purchase #4	$131.44	6.338%	$139.7707	$139.77	$139.75	$139.80
Purchase #5	$119.75	12.144%	$134.2924	$134.29	$134.30	$134.30
Purchase #6	$109.48	4.541%	$114.4515	$114.45	$114.45	$114.50
Purchase #7	$36.85	9.825%	$40.4705	$40.47	$40.45	$40.50
7 purchase totals =	$591.36		$636.6100	$636.61	$636.55	$636.70