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	$18.95	13.116%	$21.4355	$21.44	$21.45	$21.40
Purchase #2	$243.73	5.412%	$256.9207	$256.92	$256.90	$256.90
Purchase #3	$101.76	4.516%	$106.3555	$106.36	$106.35	$106.40
Purchase #4	$23.56	11.723%	$26.3219	$26.32	$26.30	$26.30
Purchase #5	$42.71	10.720%	$47.2885	$47.29	$47.30	$47.30
Purchase #6	$71.57	9.217%	$78.1666	$78.17	$78.15	$78.20
Purchase #7	$167.69	10.578%	$185.4282	$185.43	$185.45	$185.40
7 purchase totals =	$669.97		$721.9169	$721.93	$721.90	$721.90