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	$73.39	10.172%	$80.8552	$80.86	$80.85	$80.90
Purchase #2	$101.70	12.361%	$114.2711	$114.27	$114.25	$114.30
Purchase #3	$46.51	11.621%	$51.9149	$51.91	$51.90	$51.90
Purchase #4	$117.32	10.691%	$129.8627	$129.86	$129.85	$129.90
Purchase #5	$106.43	6.711%	$113.5725	$113.57	$113.55	$113.60
Purchase #6	$39.64	6.208%	$42.1009	$42.10	$42.10	$42.10
Purchase #7	$87.25	7.215%	$93.5451	$93.55	$93.55	$93.50
7 purchase totals =	$572.24		$626.1224	$626.12	$626.05	$626.20