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	$115.61	7.134%	$123.8576	$123.86	$123.85	$123.90
Purchase #2	$108.73	9.665%	$119.2388	$119.24	$119.25	$119.20
Purchase #3	$111.56	8.822%	$121.4018	$121.40	$121.40	$121.40
Purchase #4	$86.82	5.156%	$91.2964	$91.30	$91.30	$91.30
Purchase #5	$120.92	13.873%	$137.6952	$137.70	$137.70	$137.70
Purchase #6	$173.60	4.776%	$181.8911	$181.89	$181.90	$181.90
Purchase #7	$7.85	11.700%	$8.7685	$8.77	$8.75	$8.80
7 purchase totals =	$725.09		$784.1494	$784.16	$784.15	$784.20