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	$135.57	12.734%	$152.8335	$152.83	$152.85	$152.80
Purchase #2	$169.77	9.749%	$186.3209	$186.32	$186.30	$186.30
Purchase #3	$74.38	11.328%	$82.8058	$82.81	$82.80	$82.80
Purchase #4	$109.42	12.840%	$123.4695	$123.47	$123.45	$123.50
Purchase #5	$11.83	11.130%	$13.1467	$13.15	$13.15	$13.10
Purchase #6	$82.91	3.355%	$85.6916	$85.69	$85.70	$85.70
Purchase #7	$77.88	7.120%	$83.4251	$83.43	$83.45	$83.40
7 purchase totals =	$661.76		$727.6931	$727.70	$727.70	$727.60