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	$203.86	8.570%	$221.3308	$221.33	$221.35	$221.30
Purchase #2	$84.85	12.506%	$95.4613	$95.46	$95.45	$95.50
Purchase #3	$250.42	13.714%	$284.7626	$284.76	$284.75	$284.80
Purchase #4	$33.65	5.526%	$35.5095	$35.51	$35.50	$35.50
Purchase #5	$73.88	7.158%	$79.1683	$79.17	$79.15	$79.20
Purchase #6	$18.95	12.302%	$21.2812	$21.28	$21.30	$21.30
Purchase #7	$163.69	5.274%	$172.323	$172.32	$172.30	$172.30
7 purchase totals =	$829.30		$909.8367	$909.83	$909.80	$909.90