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	$98.26	7.277%	$105.4104	$105.41	$105.40	$105.40
Purchase #2	$196.48	10.702%	$217.5073	$217.51	$217.50	$217.50
Purchase #3	$37.65	12.265%	$42.2678	$42.27	$42.25	$42.30
Purchase #4	$135.30	9.274%	$147.8477	$147.85	$147.85	$147.80
Purchase #5	$39.41	4.116%	$41.0321	$41.03	$41.05	$41.00
Purchase #6	$54.45	12.871%	$61.4583	$61.46	$61.45	$61.50
Purchase #7	$28.46	4.217%	$29.6602	$29.66	$29.65	$29.70
7 purchase totals =	$590.01		$645.1838	$645.19	$645.15	$645.20