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	$231.83	4.758%	$242.8605	$242.86	$242.85	$242.90
Purchase #2	$222.89	7.682%	$240.0124	$240.01	$240.00	$240.00
Purchase #3	$131.55	4.425%	$137.3711	$137.37	$137.35	$137.40
Purchase #4	$92.79	6.797%	$99.0969	$99.10	$99.10	$99.10
Purchase #5	$65.94	5.134%	$69.3254	$69.33	$69.35	$69.30
Purchase #6	$18.80	12.262%	$21.1053	$21.11	$21.10	$21.10
Purchase #7	$107.97	10.570%	$119.3824	$119.38	$119.40	$119.40
7 purchase totals =	$871.77		$929.1540	$929.16	$929.15	$929.20