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	$89.97	3.119%	$92.7762	$92.78	$92.80	$92.80
Purchase #2	$118.60	8.392%	$128.5529	$128.55	$128.55	$128.60
Purchase #3	$60.65	3.515%	$62.7818	$62.78	$62.80	$62.80
Purchase #4	$183.38	3.707%	$190.1779	$190.18	$190.20	$190.20
Purchase #5	$110.98	11.354%	$123.5807	$123.58	$123.60	$123.60
Purchase #6	$71.62	11.734%	$80.0239	$80.02	$80.00	$80.00
Purchase #7	$164.92	6.670%	$175.9202	$175.92	$175.90	$175.90
7 purchase totals =	$800.12		$853.8136	$853.81	$853.85	$853.90