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	$217.39	6.333%	$231.1573	$231.16	$231.15	$231.20
Purchase #2	$80.81	11.279%	$89.9246	$89.92	$89.90	$89.90
Purchase #3	$103.33	10.685%	$114.3708	$114.37	$114.35	$114.40
Purchase #4	$219.92	5.178%	$231.3075	$231.31	$231.30	$231.30
Purchase #5	$21.30	5.400%	$22.4502	$22.45	$22.45	$22.50
Purchase #6	$13.36	8.689%	$14.5209	$14.52	$14.50	$14.50
Purchase #7	$60.37	7.310%	$64.783	$64.78	$64.80	$64.80
7 purchase totals =	$716.48		$768.5143	$768.51	$768.45	$768.60