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	$52.79	11.868%	$59.0551	$59.06	$59.05	$59.10
Purchase #2	$42.76	12.463%	$48.0892	$48.09	$48.10	$48.10
Purchase #3	$115.38	8.575%	$125.2738	$125.27	$125.25	$125.30
Purchase #4	$30.74	3.484%	$31.811	$31.81	$31.80	$31.80
Purchase #5	$55.53	3.215%	$57.3153	$57.32	$57.30	$57.30
Purchase #6	$12.88	10.518%	$14.2347	$14.23	$14.25	$14.20
Purchase #7	$233.33	10.625%	$258.1213	$258.12	$258.10	$258.10
7 purchase totals =	$543.41		$593.9004	$593.90	$593.85	$593.90