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	$99.67	4.741%	$104.3954	$104.40	$104.40	$104.40
Purchase #2	$45.56	10.143%	$50.1812	$50.18	$50.20	$50.20
Purchase #3	$98.66	6.761%	$105.3304	$105.33	$105.35	$105.30
Purchase #4	$111.56	8.339%	$120.863	$120.86	$120.85	$120.90
Purchase #5	$220.70	8.568%	$239.6096	$239.61	$239.60	$239.60
Purchase #6	$113.54	3.499%	$117.5128	$117.51	$117.50	$117.50
Purchase #7	$98.33	7.498%	$105.7028	$105.70	$105.70	$105.70
7 purchase totals =	$788.02		$843.5952	$843.59	$843.60	$843.60