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	$173.46	7.223%	$185.989	$185.99	$186.00	$186.00
Purchase #2	$143.34	11.807%	$160.2642	$160.26	$160.25	$160.30
Purchase #3	$44.82	5.432%	$47.2546	$47.25	$47.25	$47.30
Purchase #4	$89.32	12.860%	$100.8066	$100.81	$100.80	$100.80
Purchase #5	$172.38	11.283%	$191.8296	$191.83	$191.85	$191.80
Purchase #6	$36.91	5.698%	$39.0131	$39.01	$39.00	$39.00
Purchase #7	$128.39	11.723%	$143.4412	$143.44	$143.45	$143.40
7 purchase totals =	$788.62		$868.5983	$868.59	$868.60	$868.60