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	$163.55	13.602%	$185.7961	$185.80	$185.80	$185.80
Purchase #2	$206.71	4.109%	$215.2037	$215.20	$215.20	$215.20
Purchase #3	$208.67	8.187%	$225.7538	$225.75	$225.75	$225.80
Purchase #4	$82.28	8.760%	$89.4877	$89.49	$89.50	$89.50
Purchase #5	$77.59	10.399%	$85.6586	$85.66	$85.65	$85.70
Purchase #6	$18.45	4.415%	$19.2646	$19.26	$19.25	$19.30
Purchase #7	$20.41	5.639%	$21.5609	$21.56	$21.55	$21.60
7 purchase totals =	$777.66		$842.7254	$842.72	$842.70	$842.90