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	$98.67	11.754%	$110.2677	$110.27	$110.25	$110.30
Purchase #2	$42.35	5.682%	$44.7563	$44.76	$44.75	$44.80
Purchase #3	$82.29	13.695%	$93.5596	$93.56	$93.55	$93.60
Purchase #4	$16.89	8.172%	$18.2703	$18.27	$18.25	$18.30
Purchase #5	$118.97	10.451%	$131.4036	$131.40	$131.40	$131.40
Purchase #6	$105.48	3.229%	$108.8859	$108.89	$108.90	$108.90
Purchase #7	$155.49	4.720%	$162.8291	$162.83	$162.85	$162.80
7 purchase totals =	$620.14		$669.9725	$669.98	$669.95	$670.10