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	$12.45	8.517%	$13.5104	$13.51	$13.50	$13.50
Purchase #2	$115.38	4.795%	$120.9125	$120.91	$120.90	$120.90
Purchase #3	$137.31	10.650%	$151.9335	$151.93	$151.95	$151.90
Purchase #4	$250.48	9.307%	$273.7922	$273.79	$273.80	$273.80
Purchase #5	$150.37	10.667%	$166.41	$166.41	$166.40	$166.40
Purchase #6	$223.50	7.587%	$240.4569	$240.46	$240.45	$240.50
Purchase #7	$199.62	9.290%	$218.1647	$218.16	$218.15	$218.20
7 purchase totals =	$1,089.11		$1,185.1802	$1,185.17	$1,185.15	$1,185.20