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	$221.40	4.746%	$231.9076	$231.91	$231.90	$231.90
Purchase #2	$112.46	9.620%	$123.2787	$123.28	$123.30	$123.30
Purchase #3	$164.39	10.629%	$181.863	$181.86	$181.85	$181.90
Purchase #4	$89.61	4.149%	$93.3279	$93.33	$93.35	$93.30
Purchase #5	$13.50	3.198%	$13.9317	$13.93	$13.95	$13.90
Purchase #6	$111.48	11.134%	$123.8922	$123.89	$123.90	$123.90
Purchase #7	$100.98	13.855%	$114.9708	$114.97	$114.95	$115.00
7 purchase totals =	$813.82		$883.1719	$883.17	$883.20	$883.20