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	$112.89	12.695%	$127.2214	$127.22	$127.20	$127.20
Purchase #2	$139.71	9.751%	$153.3331	$153.33	$153.35	$153.30
Purchase #3	$43.72	10.396%	$48.2651	$48.27	$48.25	$48.30
Purchase #4	$160.38	9.744%	$176.0074	$176.01	$176.00	$176.00
Purchase #5	$48.57	12.117%	$54.4552	$54.46	$54.45	$54.50
Purchase #6	$33.59	10.505%	$37.1186	$37.12	$37.10	$37.10
Purchase #7	$81.47	13.462%	$92.4375	$92.44	$92.45	$92.40
7 purchase totals =	$620.33		$688.8383	$688.85	$688.80	$688.80