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	$137.70	8.728%	$149.7185	$149.72	$149.70	$149.70
Purchase #2	$114.94	12.177%	$128.9362	$128.94	$128.95	$128.90
Purchase #3	$37.96	6.376%	$40.3803	$40.38	$40.40	$40.40
Purchase #4	$78.74	13.697%	$89.525	$89.53	$89.55	$89.50
Purchase #5	$90.87	9.511%	$99.5126	$99.51	$99.50	$99.50
Purchase #6	$166.44	4.685%	$174.2377	$174.24	$174.25	$174.20
Purchase #7	$119.47	3.485%	$123.6335	$123.63	$123.65	$123.60
7 purchase totals =	$746.12		$805.9438	$805.95	$806.00	$805.80