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	$71.94	8.213%	$77.8484	$77.85	$77.85	$77.80
Purchase #2	$119.55	3.251%	$123.4366	$123.44	$123.45	$123.40
Purchase #3	$133.41	12.351%	$149.8875	$149.89	$149.90	$149.90
Purchase #4	$112.75	9.313%	$123.2504	$123.25	$123.25	$123.30
Purchase #5	$154.82	10.484%	$171.0513	$171.05	$171.05	$171.10
Purchase #6	$81.89	5.674%	$86.5364	$86.54	$86.55	$86.50
Purchase #7	$99.97	3.782%	$103.7509	$103.75	$103.75	$103.80
7 purchase totals =	$774.33		$835.7615	$835.77	$835.80	$835.80