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	$246.58	3.134%	$254.3078	$254.31	$254.30	$254.30
Purchase #2	$19.72	13.766%	$22.4347	$22.43	$22.45	$22.40
Purchase #3	$92.60	11.333%	$103.0944	$103.09	$103.10	$103.10
Purchase #4	$139.49	6.342%	$148.3365	$148.34	$148.35	$148.30
Purchase #5	$139.26	9.314%	$152.2307	$152.23	$152.25	$152.20
Purchase #6	$79.95	8.690%	$86.8977	$86.90	$86.90	$86.90
Purchase #7	$207.55	4.529%	$216.9499	$216.95	$216.95	$216.90
7 purchase totals =	$925.15		$984.2517	$984.25	$984.30	$984.10