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	$72.33	9.459%	$79.1717	$79.17	$79.15	$79.20
Purchase #2	$90.82	12.776%	$102.4232	$102.42	$102.40	$102.40
Purchase #3	$143.94	3.410%	$148.8484	$148.85	$148.85	$148.80
Purchase #4	$246.98	4.584%	$258.3016	$258.30	$258.30	$258.30
Purchase #5	$173.90	9.173%	$189.8518	$189.85	$189.85	$189.90
Purchase #6	$196.41	12.731%	$221.415	$221.42	$221.40	$221.40
Purchase #7	$147.45	12.182%	$165.4124	$165.41	$165.40	$165.40
7 purchase totals =	$1,071.83		$1,165.4241	$1,165.42	$1,165.35	$1,165.40