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	$101.76	6.775%	$108.6542	$108.65	$108.65	$108.70
Purchase #2	$171.25	11.697%	$191.2811	$191.28	$191.30	$191.30
Purchase #3	$109.65	12.297%	$123.1337	$123.13	$123.15	$123.10
Purchase #4	$91.32	12.845%	$103.0501	$103.05	$103.05	$103.10
Purchase #5	$35.87	10.224%	$39.5373	$39.54	$39.55	$39.50
Purchase #6	$215.50	7.147%	$230.9018	$230.90	$230.90	$230.90
Purchase #7	$110.96	12.280%	$124.5859	$124.59	$124.60	$124.60
7 purchase totals =	$836.31		$921.1441	$921.14	$921.20	$921.20