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	$109.73	12.409%	$123.3464	$123.35	$123.35	$123.30
Purchase #2	$220.72	6.209%	$234.4245	$234.42	$234.40	$234.40
Purchase #3	$43.29	10.752%	$47.9445	$47.94	$47.95	$47.90
Purchase #4	$39.51	10.756%	$43.7597	$43.76	$43.75	$43.80
Purchase #5	$234.57	11.538%	$261.6347	$261.63	$261.65	$261.60
Purchase #6	$109.72	6.794%	$117.1744	$117.17	$117.15	$117.20
Purchase #7	$10.63	9.282%	$11.6167	$11.62	$11.60	$11.60
7 purchase totals =	$768.17		$839.9009	$839.89	$839.85	$839.80