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	$72.84	7.871%	$78.5732	$78.57	$78.55	$78.60
Purchase #2	$189.85	3.675%	$196.827	$196.83	$196.85	$196.80
Purchase #3	$204.70	13.523%	$232.3816	$232.38	$232.40	$232.40
Purchase #4	$154.46	3.384%	$159.6869	$159.69	$159.70	$159.70
Purchase #5	$92.80	3.242%	$95.8086	$95.81	$95.80	$95.80
Purchase #6	$73.48	12.298%	$82.5166	$82.52	$82.50	$82.50
Purchase #7	$65.47	7.245%	$70.2133	$70.21	$70.20	$70.20
7 purchase totals =	$853.60		$916.0072	$916.01	$916.00	$916.00