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	$125.75	6.754%	$134.2432	$134.24	$134.25	$134.20
Purchase #2	$141.50	7.231%	$151.7319	$151.73	$151.75	$151.70
Purchase #3	$198.47	11.382%	$221.0599	$221.06	$221.05	$221.10
Purchase #4	$14.37	8.341%	$15.5686	$15.57	$15.55	$15.60
Purchase #5	$63.98	12.608%	$72.0466	$72.05	$72.05	$72.00
Purchase #6	$195.44	5.349%	$205.8941	$205.89	$205.90	$205.90
Purchase #7	$230.85	3.353%	$238.5904	$238.59	$238.60	$238.60
7 purchase totals =	$970.36		$1,039.1347	$1,039.13	$1,039.15	$1,039.10