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	$75.42	11.816%	$84.3316	$84.33	$84.35	$84.30
Purchase #2	$234.39	13.308%	$265.5826	$265.58	$265.60	$265.60
Purchase #3	$126.26	13.862%	$143.7622	$143.76	$143.75	$143.80
Purchase #4	$53.45	6.675%	$57.0178	$57.02	$57.00	$57.00
Purchase #5	$99.43	4.171%	$103.5772	$103.58	$103.60	$103.60
Purchase #6	$161.38	12.127%	$180.9506	$180.95	$180.95	$181.00
Purchase #7	$158.88	5.139%	$167.0448	$167.04	$167.05	$167.00
7 purchase totals =	$909.21		$1,002.2668	$1,002.26	$1,002.30	$1,002.30