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	$146.86	12.744%	$165.5758	$165.58	$165.60	$165.60
Purchase #2	$89.37	7.522%	$96.0924	$96.09	$96.10	$96.10
Purchase #3	$88.75	10.702%	$98.248	$98.25	$98.25	$98.20
Purchase #4	$48.72	3.122%	$50.241	$50.24	$50.25	$50.20
Purchase #5	$66.66	4.154%	$69.4291	$69.43	$69.45	$69.40
Purchase #6	$156.53	7.395%	$168.1054	$168.11	$168.10	$168.10
Purchase #7	$199.78	11.286%	$222.3272	$222.33	$222.35	$222.30
7 purchase totals =	$796.67		$870.0189	$870.03	$870.10	$869.90