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	$218.44	4.206%	$227.6276	$227.63	$227.65	$227.60
Purchase #2	$146.40	6.465%	$155.8648	$155.86	$155.85	$155.90
Purchase #3	$111.98	9.386%	$122.4904	$122.49	$122.50	$122.50
Purchase #4	$189.53	3.717%	$196.5748	$196.57	$196.55	$196.60
Purchase #5	$37.27	12.792%	$42.0376	$42.04	$42.05	$42.00
Purchase #6	$138.69	5.294%	$146.0322	$146.03	$146.05	$146.00
Purchase #7	$38.45	13.670%	$43.7061	$43.71	$43.70	$43.70
7 purchase totals =	$880.76		$934.3335	$934.33	$934.35	$934.30