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	$126.60	12.417%	$142.3199	$142.32	$142.30	$142.30
Purchase #2	$82.52	6.331%	$87.7443	$87.74	$87.75	$87.70
Purchase #3	$91.78	12.448%	$103.2048	$103.20	$103.20	$103.20
Purchase #4	$24.63	13.164%	$27.8723	$27.87	$27.85	$27.90
Purchase #5	$48.50	11.564%	$54.1085	$54.11	$54.10	$54.10
Purchase #6	$82.66	12.331%	$92.8528	$92.85	$92.85	$92.90
Purchase #7	$82.77	12.252%	$92.911	$92.91	$92.90	$92.90
7 purchase totals =	$539.46		$601.0136	$601.00	$600.95	$601.00