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	$107.26	12.273%	$120.424	$120.42	$120.40	$120.40
Purchase #2	$245.31	11.832%	$274.3351	$274.34	$274.35	$274.30
Purchase #3	$71.38	9.444%	$78.1211	$78.12	$78.10	$78.10
Purchase #4	$182.97	9.793%	$200.8883	$200.89	$200.90	$200.90
Purchase #5	$101.36	12.295%	$113.8222	$113.82	$113.80	$113.80
Purchase #6	$13.88	4.852%	$14.5535	$14.55	$14.55	$14.60
Purchase #7	$72.53	9.635%	$79.5183	$79.52	$79.50	$79.50
7 purchase totals =	$794.69		$881.6625	$881.66	$881.60	$881.60