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	$62.94	13.237%	$71.2714	$71.27	$71.25	$71.30
Purchase #2	$148.42	12.334%	$166.7261	$166.73	$166.75	$166.70
Purchase #3	$150.45	10.475%	$166.2096	$166.21	$166.20	$166.20
Purchase #4	$158.41	8.433%	$171.7687	$171.77	$171.75	$171.80
Purchase #5	$176.99	10.814%	$196.1297	$196.13	$196.15	$196.10
Purchase #6	$24.63	4.735%	$25.7962	$25.80	$25.80	$25.80
Purchase #7	$136.26	6.657%	$145.3308	$145.33	$145.35	$145.30
7 purchase totals =	$858.10		$943.2325	$943.24	$943.25	$943.20