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	$93.54	6.317%	$99.4489	$99.45	$99.45	$99.40
Purchase #2	$85.40	4.265%	$89.0423	$89.04	$89.05	$89.00
Purchase #3	$5.38	12.355%	$6.0447	$6.04	$6.05	$6.00
Purchase #4	$144.30	9.178%	$157.5439	$157.54	$157.55	$157.50
Purchase #5	$135.72	3.348%	$140.2639	$140.26	$140.25	$140.30
Purchase #6	$151.55	7.422%	$162.798	$162.80	$162.80	$162.80
Purchase #7	$85.57	5.732%	$90.4749	$90.47	$90.45	$90.50
7 purchase totals =	$701.46		$745.6166	$745.60	$745.60	$745.50