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	$79.74	9.588%	$87.3855	$87.39	$87.40	$87.40
Purchase #2	$197.33	13.463%	$223.8965	$223.90	$223.90	$223.90
Purchase #3	$59.61	4.405%	$62.2358	$62.24	$62.25	$62.20
Purchase #4	$43.25	4.117%	$45.0306	$45.03	$45.05	$45.00
Purchase #5	$109.60	12.177%	$122.946	$122.95	$122.95	$122.90
Purchase #6	$218.94	5.792%	$231.621	$231.62	$231.60	$231.60
Purchase #7	$83.79	7.238%	$89.8547	$89.85	$89.85	$89.90
7 purchase totals =	$792.26		$862.9701	$862.98	$863.00	$862.90