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	$18.47	11.635%	$20.619	$20.62	$20.60	$20.60
Purchase #2	$245.89	11.118%	$273.2281	$273.23	$273.25	$273.20
Purchase #3	$116.75	12.725%	$131.6064	$131.61	$131.60	$131.60
Purchase #4	$111.32	12.855%	$125.6302	$125.63	$125.65	$125.60
Purchase #5	$67.54	6.150%	$71.6937	$71.69	$71.70	$71.70
Purchase #6	$101.52	8.793%	$110.4467	$110.45	$110.45	$110.40
Purchase #7	$238.85	10.134%	$263.0551	$263.06	$263.05	$263.10
7 purchase totals =	$900.34		$996.2792	$996.29	$996.30	$996.20