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	$51.77	8.764%	$56.3071	$56.31	$56.30	$56.30
Purchase #2	$171.68	4.210%	$178.9077	$178.91	$178.90	$178.90
Purchase #3	$221.61	10.790%	$245.5217	$245.52	$245.50	$245.50
Purchase #4	$24.96	10.372%	$27.5489	$27.55	$27.55	$27.50
Purchase #5	$141.59	12.116%	$158.745	$158.75	$158.75	$158.70
Purchase #6	$82.27	11.401%	$91.6496	$91.65	$91.65	$91.60
Purchase #7	$202.50	13.322%	$229.4771	$229.48	$229.50	$229.50
7 purchase totals =	$896.38		$988.1571	$988.17	$988.15	$988.00