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	$95.77	3.752%	$99.3633	$99.36	$99.35	$99.40
Purchase #2	$130.79	12.170%	$146.7071	$146.71	$146.70	$146.70
Purchase #3	$10.67	10.618%	$11.8029	$11.80	$11.80	$11.80
Purchase #4	$120.90	4.397%	$126.216	$126.22	$126.20	$126.20
Purchase #5	$40.55	5.740%	$42.8776	$42.88	$42.90	$42.90
Purchase #6	$167.43	3.263%	$172.8932	$172.89	$172.90	$172.90
Purchase #7	$234.98	9.572%	$257.4723	$257.47	$257.45	$257.50
7 purchase totals =	$801.09		$857.3324	$857.33	$857.30	$857.40