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	$183.78	3.159%	$189.5856	$189.59	$189.60	$189.60
Purchase #2	$79.28	3.623%	$82.1523	$82.15	$82.15	$82.20
Purchase #3	$101.57	3.709%	$105.3372	$105.34	$105.35	$105.30
Purchase #4	$100.36	4.593%	$104.9695	$104.97	$104.95	$105.00
Purchase #5	$243.83	12.109%	$273.3554	$273.36	$273.35	$273.40
Purchase #6	$187.26	9.528%	$205.1021	$205.10	$205.10	$205.10
Purchase #7	$19.38	11.775%	$21.662	$21.66	$21.65	$21.70
7 purchase totals =	$915.46		$982.1641	$982.17	$982.15	$982.30