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	$35.93	5.531%	$37.9173	$37.92	$37.90	$37.90
Purchase #2	$107.33	4.149%	$111.7831	$111.78	$111.80	$111.80
Purchase #3	$209.28	12.315%	$235.0528	$235.05	$235.05	$235.10
Purchase #4	$201.39	8.762%	$219.0358	$219.04	$219.05	$219.00
Purchase #5	$75.95	6.796%	$81.1116	$81.11	$81.10	$81.10
Purchase #6	$125.29	5.285%	$131.9116	$131.91	$131.90	$131.90
Purchase #7	$173.33	4.729%	$181.5268	$181.53	$181.55	$181.50
7 purchase totals =	$928.50		$998.3390	$998.34	$998.35	$998.30