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	$39.69	7.493%	$42.664	$42.66	$42.65	$42.70
Purchase #2	$99.57	12.648%	$112.1636	$112.16	$112.15	$112.20
Purchase #3	$211.41	12.515%	$237.868	$237.87	$237.85	$237.90
Purchase #4	$49.75	5.454%	$52.4634	$52.46	$52.45	$52.50
Purchase #5	$75.67	9.429%	$82.8049	$82.80	$82.80	$82.80
Purchase #6	$132.71	13.270%	$150.3206	$150.32	$150.30	$150.30
Purchase #7	$168.67	10.766%	$186.829	$186.83	$186.85	$186.80
7 purchase totals =	$777.47		$865.1135	$865.10	$865.05	$865.20