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	$76.86	12.693%	$86.6158	$86.62	$86.60	$86.60
Purchase #2	$165.53	11.786%	$185.0394	$185.04	$185.05	$185.00
Purchase #3	$44.86	12.815%	$50.6088	$50.61	$50.60	$50.60
Purchase #4	$175.58	6.265%	$186.5801	$186.58	$186.60	$186.60
Purchase #5	$84.95	6.324%	$90.3222	$90.32	$90.30	$90.30
Purchase #6	$237.73	5.435%	$250.6506	$250.65	$250.65	$250.70
Purchase #7	$111.37	6.624%	$118.7471	$118.75	$118.75	$118.70
7 purchase totals =	$896.88		$968.5640	$968.57	$968.55	$968.50