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	$7.96	11.504%	$8.8757	$8.88	$8.90	$8.90
Purchase #2	$38.62	10.656%	$42.7353	$42.74	$42.75	$42.70
Purchase #3	$132.27	4.287%	$137.9404	$137.94	$137.95	$137.90
Purchase #4	$102.94	11.657%	$114.9397	$114.94	$114.95	$114.90
Purchase #5	$190.56	11.730%	$212.9127	$212.91	$212.90	$212.90
Purchase #6	$17.35	10.464%	$19.1655	$19.17	$19.15	$19.20
Purchase #7	$190.64	3.231%	$196.7996	$196.80	$196.80	$196.80
7 purchase totals =	$680.34		$733.3689	$733.38	$733.40	$733.30