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	$128.63	4.588%	$134.5315	$134.53	$134.55	$134.50
Purchase #2	$163.75	8.401%	$177.5066	$177.51	$177.50	$177.50
Purchase #3	$178.58	6.109%	$189.4895	$189.49	$189.50	$189.50
Purchase #4	$160.88	3.192%	$166.0153	$166.02	$166.00	$166.00
Purchase #5	$11.94	4.869%	$12.5214	$12.52	$12.50	$12.50
Purchase #6	$35.55	5.387%	$37.4651	$37.47	$37.45	$37.50
Purchase #7	$63.81	13.563%	$72.4646	$72.46	$72.45	$72.50
7 purchase totals =	$743.14		$789.9940	$790.00	$789.95	$790.00