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	$140.66	11.588%	$156.9597	$156.96	$156.95	$157.00
Purchase #2	$204.73	5.790%	$216.5839	$216.58	$216.60	$216.60
Purchase #3	$153.75	11.496%	$171.4251	$171.43	$171.45	$171.40
Purchase #4	$33.48	9.246%	$36.5756	$36.58	$36.60	$36.60
Purchase #5	$37.54	12.315%	$42.1631	$42.16	$42.15	$42.20
Purchase #6	$104.56	9.660%	$114.6605	$114.66	$114.65	$114.70
Purchase #7	$39.56	3.173%	$40.8152	$40.82	$40.80	$40.80
7 purchase totals =	$714.28		$779.1831	$779.19	$779.20	$779.30