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	$92.71	13.600%	$105.3186	$105.32	$105.30	$105.30
Purchase #2	$77.73	7.850%	$83.8318	$83.83	$83.85	$83.80
Purchase #3	$31.52	7.778%	$33.9716	$33.97	$33.95	$34.00
Purchase #4	$77.83	5.373%	$82.0118	$82.01	$82.00	$82.00
Purchase #5	$240.26	3.798%	$249.3851	$249.39	$249.40	$249.40
Purchase #6	$140.94	8.790%	$153.3286	$153.33	$153.35	$153.30
Purchase #7	$123.37	6.685%	$131.6173	$131.62	$131.60	$131.60
7 purchase totals =	$784.36		$839.4648	$839.47	$839.45	$839.40