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	$37.96	12.592%	$42.7399	$42.74	$42.75	$42.70
Purchase #2	$7.40	4.656%	$7.7445	$7.74	$7.75	$7.70
Purchase #3	$93.89	12.835%	$105.9408	$105.94	$105.95	$105.90
Purchase #4	$243.58	13.423%	$276.2757	$276.28	$276.30	$276.30
Purchase #5	$110.99	13.439%	$125.9059	$125.91	$125.90	$125.90
Purchase #6	$72.60	13.108%	$82.1164	$82.12	$82.10	$82.10
Purchase #7	$152.66	7.771%	$164.5232	$164.52	$164.50	$164.50
7 purchase totals =	$719.08		$805.2464	$805.25	$805.25	$805.10