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	$133.73	5.837%	$141.5358	$141.54	$141.55	$141.50
Purchase #2	$158.94	5.790%	$168.1426	$168.14	$168.15	$168.10
Purchase #3	$194.87	5.117%	$204.8415	$204.84	$204.85	$204.80
Purchase #4	$146.93	3.615%	$152.2415	$152.24	$152.25	$152.20
Purchase #5	$83.26	8.488%	$90.3271	$90.33	$90.35	$90.30
Purchase #6	$121.98	13.119%	$137.9826	$137.98	$138.00	$138.00
Purchase #7	$179.93	6.844%	$192.2444	$192.24	$192.25	$192.20
7 purchase totals =	$1,019.64		$1,087.3155	$1,087.31	$1,087.40	$1,087.10