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	$236.32	7.402%	$253.8124	$253.81	$253.80	$253.80
Purchase #2	$85.37	5.639%	$90.184	$90.18	$90.20	$90.20
Purchase #3	$205.29	11.841%	$229.5984	$229.60	$229.60	$229.60
Purchase #4	$200.93	3.466%	$207.8942	$207.89	$207.90	$207.90
Purchase #5	$60.47	10.567%	$66.8599	$66.86	$66.85	$66.90
Purchase #6	$29.62	13.260%	$33.5476	$33.55	$33.55	$33.50
Purchase #7	$109.60	4.424%	$114.4487	$114.45	$114.45	$114.40
7 purchase totals =	$927.60		$996.3452	$996.34	$996.35	$996.30