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	$234.41	10.445%	$258.8941	$258.89	$258.90	$258.90
Purchase #2	$65.90	3.623%	$68.2876	$68.29	$68.30	$68.30
Purchase #3	$168.96	13.183%	$191.234	$191.23	$191.25	$191.20
Purchase #4	$133.78	12.700%	$150.7701	$150.77	$150.75	$150.80
Purchase #5	$146.58	3.484%	$151.6868	$151.69	$151.70	$151.70
Purchase #6	$193.64	10.856%	$214.6616	$214.66	$214.65	$214.70
Purchase #7	$105.35	3.743%	$109.2933	$109.29	$109.30	$109.30
7 purchase totals =	$1,048.62		$1,144.8275	$1,144.82	$1,144.85	$1,144.90