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	$99.75	9.310%	$109.0367	$109.04	$109.05	$109.00
Purchase #2	$29.54	4.823%	$30.9647	$30.96	$30.95	$31.00
Purchase #3	$59.72	3.168%	$61.6119	$61.61	$61.60	$61.60
Purchase #4	$162.40	7.217%	$174.1204	$174.12	$174.10	$174.10
Purchase #5	$238.40	6.322%	$253.4716	$253.47	$253.45	$253.50
Purchase #6	$65.39	9.240%	$71.432	$71.43	$71.45	$71.40
Purchase #7	$158.69	4.819%	$166.3373	$166.34	$166.35	$166.30
7 purchase totals =	$813.89		$866.9746	$866.97	$866.95	$866.90