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	$132.38	5.672%	$139.8886	$139.89	$139.90	$139.90
Purchase #2	$145.56	3.725%	$150.9821	$150.98	$151.00	$151.00
Purchase #3	$215.30	6.632%	$229.5787	$229.58	$229.60	$229.60
Purchase #4	$217.89	13.385%	$247.0546	$247.05	$247.05	$247.10
Purchase #5	$235.34	3.275%	$243.0474	$243.05	$243.05	$243.00
Purchase #6	$67.48	8.757%	$73.3892	$73.39	$73.40	$73.40
Purchase #7	$14.42	4.553%	$15.0765	$15.08	$15.10	$15.10
7 purchase totals =	$1,028.37		$1,099.0171	$1,099.02	$1,099.10	$1,099.10