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	$97.28	12.518%	$109.4575	$109.46	$109.45	$109.50
Purchase #2	$189.59	3.808%	$196.8096	$196.81	$196.80	$196.80
Purchase #3	$74.93	10.263%	$82.6201	$82.62	$82.60	$82.60
Purchase #4	$90.57	11.524%	$101.0073	$101.01	$101.00	$101.00
Purchase #5	$67.51	4.774%	$70.7329	$70.73	$70.75	$70.70
Purchase #6	$61.55	10.610%	$68.0805	$68.08	$68.10	$68.10
Purchase #7	$207.41	13.674%	$235.7712	$235.77	$235.75	$235.80
7 purchase totals =	$788.84		$864.4791	$864.48	$864.45	$864.50