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	$46.97	7.533%	$50.5083	$50.51	$50.50	$50.50
Purchase #2	$235.62	6.266%	$250.3839	$250.38	$250.40	$250.40
Purchase #3	$123.87	8.700%	$134.6467	$134.65	$134.65	$134.60
Purchase #4	$146.52	7.389%	$157.3464	$157.35	$157.35	$157.30
Purchase #5	$203.54	5.861%	$215.4695	$215.47	$215.45	$215.50
Purchase #6	$28.54	9.664%	$31.2981	$31.30	$31.30	$31.30
Purchase #7	$248.56	6.167%	$263.8887	$263.89	$263.90	$263.90
7 purchase totals =	$1,033.62		$1,103.5416	$1,103.55	$1,103.55	$1,103.50