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	$224.57	9.754%	$246.4746	$246.47	$246.45	$246.50
Purchase #2	$42.51	10.544%	$46.9923	$46.99	$47.00	$47.00
Purchase #3	$128.90	6.253%	$136.9601	$136.96	$136.95	$137.00
Purchase #4	$64.71	4.779%	$67.8025	$67.80	$67.80	$67.80
Purchase #5	$165.51	12.299%	$185.8661	$185.87	$185.85	$185.90
Purchase #6	$75.38	13.508%	$85.5623	$85.56	$85.55	$85.60
Purchase #7	$151.44	4.646%	$158.4759	$158.48	$158.50	$158.50
7 purchase totals =	$853.02		$928.1338	$928.13	$928.10	$928.30