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	$104.81	11.353%	$116.7091	$116.71	$116.70	$116.70
Purchase #2	$74.80	10.319%	$82.5186	$82.52	$82.50	$82.50
Purchase #3	$176.33	5.388%	$185.8307	$185.83	$185.85	$185.80
Purchase #4	$24.57	12.344%	$27.6029	$27.60	$27.60	$27.60
Purchase #5	$202.67	13.362%	$229.7508	$229.75	$229.75	$229.80
Purchase #6	$81.98	4.654%	$85.7953	$85.80	$85.80	$85.80
Purchase #7	$159.64	7.490%	$171.597	$171.60	$171.60	$171.60
7 purchase totals =	$824.80		$899.8044	$899.81	$899.80	$899.80