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	$65.31	9.709%	$71.6509	$71.65	$71.65	$71.70
Purchase #2	$226.79	10.824%	$251.3377	$251.34	$251.35	$251.30
Purchase #3	$17.97	12.177%	$20.1582	$20.16	$20.15	$20.20
Purchase #4	$105.79	13.735%	$120.3203	$120.32	$120.30	$120.30
Purchase #5	$105.57	6.268%	$112.1871	$112.19	$112.20	$112.20
Purchase #6	$106.77	4.838%	$111.9355	$111.94	$111.95	$111.90
Purchase #7	$155.82	7.661%	$167.7574	$167.76	$167.75	$167.80
7 purchase totals =	$784.02		$855.3471	$855.36	$855.35	$855.40