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	$18.37	9.130%	$20.0472	$20.05	$20.05	$20.00
Purchase #2	$129.81	6.668%	$138.4657	$138.47	$138.45	$138.50
Purchase #3	$192.92	8.321%	$208.9729	$208.97	$208.95	$209.00
Purchase #4	$167.39	10.594%	$185.1233	$185.12	$185.10	$185.10
Purchase #5	$237.70	5.315%	$250.3338	$250.33	$250.35	$250.30
Purchase #6	$147.67	10.229%	$162.7752	$162.78	$162.80	$162.80
Purchase #7	$179.37	6.570%	$191.1546	$191.15	$191.15	$191.20
7 purchase totals =	$1,073.23		$1,156.8727	$1,156.87	$1,156.85	$1,156.90