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	$105.31	5.711%	$111.3243	$111.32	$111.30	$111.30
Purchase #2	$185.86	7.801%	$200.3589	$200.36	$200.35	$200.40
Purchase #3	$153.67	13.836%	$174.9318	$174.93	$174.95	$174.90
Purchase #4	$107.45	10.570%	$118.8075	$118.81	$118.80	$118.80
Purchase #5	$79.35	11.668%	$88.6086	$88.61	$88.60	$88.60
Purchase #6	$141.66	4.436%	$147.944	$147.94	$147.95	$147.90
Purchase #7	$225.66	6.181%	$239.608	$239.61	$239.60	$239.60
7 purchase totals =	$998.96		$1,081.5831	$1,081.58	$1,081.55	$1,081.50