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	$131.58	4.832%	$137.9379	$137.94	$137.95	$137.90
Purchase #2	$170.51	11.726%	$190.504	$190.50	$190.50	$190.50
Purchase #3	$76.79	8.257%	$83.1306	$83.13	$83.15	$83.10
Purchase #4	$61.68	8.627%	$67.0011	$67.00	$67.00	$67.00
Purchase #5	$210.61	9.266%	$230.1251	$230.13	$230.15	$230.10
Purchase #6	$142.43	7.338%	$152.8815	$152.88	$152.90	$152.90
Purchase #7	$241.45	6.328%	$256.729	$256.73	$256.75	$256.70
7 purchase totals =	$1,035.05		$1,118.3092	$1,118.31	$1,118.40	$1,118.20