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	$80.87	10.869%	$89.6598	$89.66	$89.65	$89.70
Purchase #2	$222.56	6.111%	$236.1606	$236.16	$236.15	$236.20
Purchase #3	$228.36	4.812%	$239.3487	$239.35	$239.35	$239.30
Purchase #4	$134.61	7.221%	$144.3302	$144.33	$144.35	$144.30
Purchase #5	$249.96	9.814%	$274.4911	$274.49	$274.50	$274.50
Purchase #6	$206.55	8.610%	$224.334	$224.33	$224.35	$224.30
Purchase #7	$43.45	8.705%	$47.2323	$47.23	$47.25	$47.20
7 purchase totals =	$1,166.36		$1,255.5567	$1,255.55	$1,255.60	$1,255.50