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	$80.35	10.103%	$88.4678	$88.47	$88.45	$88.50
Purchase #2	$57.97	10.492%	$64.0522	$64.05	$64.05	$64.10
Purchase #3	$235.34	12.286%	$264.2539	$264.25	$264.25	$264.30
Purchase #4	$148.82	3.647%	$154.2475	$154.25	$154.25	$154.20
Purchase #5	$72.68	13.503%	$82.494	$82.49	$82.50	$82.50
Purchase #6	$142.33	7.873%	$153.5356	$153.54	$153.55	$153.50
Purchase #7	$40.48	6.274%	$43.0197	$43.02	$43.00	$43.00
7 purchase totals =	$777.97		$850.0707	$850.07	$850.05	$850.10