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	$122.51	12.856%	$138.2599	$138.26	$138.25	$138.30
Purchase #2	$240.70	6.676%	$256.7691	$256.77	$256.75	$256.80
Purchase #3	$241.98	5.843%	$256.1189	$256.12	$256.10	$256.10
Purchase #4	$129.39	12.112%	$145.0617	$145.06	$145.05	$145.10
Purchase #5	$77.40	11.717%	$86.469	$86.47	$86.45	$86.50
Purchase #6	$150.46	5.219%	$158.3125	$158.31	$158.30	$158.30
Purchase #7	$100.56	8.718%	$109.3268	$109.33	$109.35	$109.30
7 purchase totals =	$1,063.00		$1,150.3179	$1,150.32	$1,150.25	$1,150.40