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	$118.99	3.597%	$123.2701	$123.27	$123.25	$123.30
Purchase #2	$121.63	5.429%	$128.2333	$128.23	$128.25	$128.20
Purchase #3	$42.89	6.824%	$45.8168	$45.82	$45.80	$45.80
Purchase #4	$69.86	12.793%	$78.7972	$78.80	$78.80	$78.80
Purchase #5	$33.62	10.558%	$37.1696	$37.17	$37.15	$37.20
Purchase #6	$149.75	12.742%	$168.8311	$168.83	$168.85	$168.80
Purchase #7	$156.97	13.603%	$178.3226	$178.32	$178.30	$178.30
7 purchase totals =	$693.71		$760.4407	$760.44	$760.40	$760.40