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	$83.67	3.246%	$86.3859	$86.39	$86.40	$86.40
Purchase #2	$76.56	6.573%	$81.5923	$81.59	$81.60	$81.60
Purchase #3	$40.60	6.328%	$43.1692	$43.17	$43.15	$43.20
Purchase #4	$172.73	13.573%	$196.1746	$196.17	$196.15	$196.20
Purchase #5	$120.47	12.512%	$135.5432	$135.54	$135.55	$135.50
Purchase #6	$81.88	8.443%	$88.7931	$88.79	$88.80	$88.80
Purchase #7	$49.63	4.680%	$51.9527	$51.95	$51.95	$52.00
7 purchase totals =	$625.54		$683.6110	$683.60	$683.60	$683.70