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	$86.74	6.691%	$92.5438	$92.54	$92.55	$92.50
Purchase #2	$150.60	6.453%	$160.3182	$160.32	$160.30	$160.30
Purchase #3	$40.97	10.629%	$45.3247	$45.32	$45.30	$45.30
Purchase #4	$243.95	4.569%	$255.0961	$255.10	$255.10	$255.10
Purchase #5	$63.45	7.401%	$68.1459	$68.15	$68.15	$68.10
Purchase #6	$154.65	10.243%	$170.4908	$170.49	$170.50	$170.50
Purchase #7	$6.50	12.720%	$7.3268	$7.33	$7.35	$7.30
7 purchase totals =	$746.86		$799.2463	$799.25	$799.25	$799.10