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	$40.50	4.542%	$42.3395	$42.34	$42.35	$42.30
Purchase #2	$73.25	7.558%	$78.7862	$78.79	$78.80	$78.80
Purchase #3	$137.90	6.294%	$146.5794	$146.58	$146.60	$146.60
Purchase #4	$181.32	8.244%	$196.268	$196.27	$196.25	$196.30
Purchase #5	$133.53	12.291%	$149.9422	$149.94	$149.95	$149.90
Purchase #6	$124.89	11.322%	$139.03	$139.03	$139.05	$139.00
Purchase #7	$80.25	13.725%	$91.2643	$91.26	$91.25	$91.30
7 purchase totals =	$771.64		$844.2096	$844.21	$844.25	$844.20