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	$123.36	5.447%	$130.0794	$130.08	$130.10	$130.10
Purchase #2	$89.61	9.668%	$98.2735	$98.27	$98.25	$98.30
Purchase #3	$117.74	12.208%	$132.1137	$132.11	$132.10	$132.10
Purchase #4	$90.99	10.363%	$100.4193	$100.42	$100.40	$100.40
Purchase #5	$53.39	11.324%	$59.4359	$59.44	$59.45	$59.40
Purchase #6	$102.78	12.713%	$115.8464	$115.85	$115.85	$115.80
Purchase #7	$155.57	10.484%	$171.88	$171.88	$171.90	$171.90
7 purchase totals =	$733.44		$808.0482	$808.05	$808.05	$808.00