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	$119.34	6.578%	$127.1902	$127.19	$127.20	$127.20
Purchase #2	$211.87	10.354%	$233.807	$233.81	$233.80	$233.80
Purchase #3	$36.40	10.774%	$40.3217	$40.32	$40.30	$40.30
Purchase #4	$65.54	3.316%	$67.7133	$67.71	$67.70	$67.70
Purchase #5	$89.49	13.390%	$101.4727	$101.47	$101.45	$101.50
Purchase #6	$20.45	8.226%	$22.1322	$22.13	$22.15	$22.10
Purchase #7	$144.41	8.562%	$156.7744	$156.77	$156.75	$156.80
7 purchase totals =	$687.50		$749.4115	$749.40	$749.35	$749.40