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	$9.90	11.745%	$11.0628	$11.06	$11.05	$11.10
Purchase #2	$39.46	3.648%	$40.8995	$40.90	$40.90	$40.90
Purchase #3	$24.58	11.511%	$27.4094	$27.41	$27.40	$27.40
Purchase #4	$33.31	4.193%	$34.7067	$34.71	$34.70	$34.70
Purchase #5	$37.67	13.560%	$42.7781	$42.78	$42.80	$42.80
Purchase #6	$121.85	10.748%	$134.9464	$134.95	$134.95	$134.90
Purchase #7	$33.83	6.144%	$35.9085	$35.91	$35.90	$35.90
7 purchase totals =	$300.60		$327.7114	$327.72	$327.70	$327.70