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	$37.98	3.498%	$39.3085	$39.31	$39.30	$39.30
Purchase #2	$35.32	3.558%	$36.5767	$36.58	$36.60	$36.60
Purchase #3	$129.38	13.553%	$146.9149	$146.91	$146.90	$146.90
Purchase #4	$153.73	5.425%	$162.0699	$162.07	$162.05	$162.10
Purchase #5	$80.45	12.687%	$90.6567	$90.66	$90.65	$90.70
Purchase #6	$186.91	6.604%	$199.2535	$199.25	$199.25	$199.30
Purchase #7	$30.82	6.554%	$32.8399	$32.84	$32.85	$32.80
7 purchase totals =	$654.59		$707.6201	$707.62	$707.60	$707.70