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	$71.68	9.674%	$78.6143	$78.61	$78.60	$78.60
Purchase #2	$164.34	8.836%	$178.8611	$178.86	$178.85	$178.90
Purchase #3	$133.89	9.637%	$146.793	$146.79	$146.80	$146.80
Purchase #4	$138.43	6.767%	$147.7976	$147.80	$147.80	$147.80
Purchase #5	$23.67	6.328%	$25.1678	$25.17	$25.15	$25.20
Purchase #6	$168.95	12.356%	$189.8255	$189.83	$189.85	$189.80
Purchase #7	$126.27	12.531%	$142.0929	$142.09	$142.10	$142.10
7 purchase totals =	$827.23		$909.1522	$909.15	$909.15	$909.20