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	$45.28	11.531%	$50.5012	$50.50	$50.50	$50.50
Purchase #2	$15.42	6.844%	$16.4753	$16.48	$16.50	$16.50
Purchase #3	$52.93	5.274%	$55.7215	$55.72	$55.70	$55.70
Purchase #4	$37.37	12.487%	$42.0364	$42.04	$42.05	$42.00
Purchase #5	$27.94	5.799%	$29.5602	$29.56	$29.55	$29.60
Purchase #6	$216.66	11.838%	$242.3082	$242.31	$242.30	$242.30
Purchase #7	$69.70	12.721%	$78.5665	$78.57	$78.55	$78.60
7 purchase totals =	$465.30		$515.1693	$515.18	$515.15	$515.20