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	$158.35	4.542%	$165.5423	$165.54	$165.55	$165.50
Purchase #2	$147.94	13.511%	$167.9282	$167.93	$167.95	$167.90
Purchase #3	$107.55	3.210%	$111.0024	$111.00	$111.00	$111.00
Purchase #4	$44.89	11.562%	$50.0802	$50.08	$50.10	$50.10
Purchase #5	$36.84	6.328%	$39.1712	$39.17	$39.15	$39.20
Purchase #6	$159.26	6.384%	$169.4272	$169.43	$169.45	$169.40
Purchase #7	$90.66	6.211%	$96.2909	$96.29	$96.30	$96.30
7 purchase totals =	$745.49		$799.4424	$799.44	$799.50	$799.40