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	$211.51	13.238%	$239.5097	$239.51	$239.50	$239.50
Purchase #2	$37.45	4.356%	$39.0813	$39.08	$39.10	$39.10
Purchase #3	$196.60	8.787%	$213.8752	$213.88	$213.90	$213.90
Purchase #4	$73.33	11.442%	$81.7204	$81.72	$81.70	$81.70
Purchase #5	$89.70	10.409%	$99.0369	$99.04	$99.05	$99.00
Purchase #6	$218.46	5.292%	$230.0209	$230.02	$230.00	$230.00
Purchase #7	$29.62	9.166%	$32.335	$32.34	$32.35	$32.30
7 purchase totals =	$856.67		$935.5794	$935.59	$935.60	$935.50