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	$228.85	8.214%	$247.6477	$247.65	$247.65	$247.60
Purchase #2	$62.97	11.483%	$70.2008	$70.20	$70.20	$70.20
Purchase #3	$179.50	6.174%	$190.5823	$190.58	$190.60	$190.60
Purchase #4	$6.33	11.579%	$7.063	$7.06	$7.05	$7.10
Purchase #5	$35.52	12.736%	$40.0438	$40.04	$40.05	$40.00
Purchase #6	$249.31	11.573%	$278.1626	$278.16	$278.15	$278.20
Purchase #7	$249.66	12.494%	$280.8525	$280.85	$280.85	$280.90
7 purchase totals =	$1,012.14		$1,114.5527	$1,114.54	$1,114.55	$1,114.60