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	$9.72	5.337%	$10.2388	$10.24	$10.25	$10.20
Purchase #2	$32.83	13.860%	$37.3802	$37.38	$37.40	$37.40
Purchase #3	$42.83	10.790%	$47.4514	$47.45	$47.45	$47.50
Purchase #4	$97.29	11.333%	$108.3159	$108.32	$108.30	$108.30
Purchase #5	$245.49	10.150%	$270.4072	$270.41	$270.40	$270.40
Purchase #6	$83.67	7.353%	$89.8223	$89.82	$89.80	$89.80
Purchase #7	$153.95	10.864%	$170.6751	$170.68	$170.70	$170.70
7 purchase totals =	$665.78		$734.2909	$734.30	$734.30	$734.30