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	$40.97	9.578%	$44.8941	$44.89	$44.90	$44.90
Purchase #2	$49.31	3.760%	$51.1641	$51.16	$51.15	$51.20
Purchase #3	$54.46	8.386%	$59.027	$59.03	$59.05	$59.00
Purchase #4	$198.58	11.107%	$220.6363	$220.64	$220.65	$220.60
Purchase #5	$127.31	13.435%	$144.4141	$144.41	$144.40	$144.40
Purchase #6	$71.45	10.630%	$79.0451	$79.05	$79.05	$79.00
Purchase #7	$104.28	7.628%	$112.2345	$112.23	$112.25	$112.20
7 purchase totals =	$646.36		$711.4152	$711.41	$711.45	$711.30