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	$160.60	12.317%	$180.3811	$180.38	$180.40	$180.40
Purchase #2	$64.27	5.529%	$67.8235	$67.82	$67.80	$67.80
Purchase #3	$124.97	12.478%	$140.5638	$140.56	$140.55	$140.60
Purchase #4	$114.99	9.667%	$126.1061	$126.11	$126.10	$126.10
Purchase #5	$107.86	3.483%	$111.6168	$111.62	$111.60	$111.60
Purchase #6	$242.73	9.103%	$264.8257	$264.83	$264.85	$264.80
Purchase #7	$136.54	4.127%	$142.175	$142.18	$142.20	$142.20
7 purchase totals =	$951.96		$1,033.4920	$1,033.50	$1,033.50	$1,033.50