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	$48.48	4.603%	$50.7115	$50.71	$50.70	$50.70
Purchase #2	$179.56	3.791%	$186.3671	$186.37	$186.35	$186.40
Purchase #3	$46.40	12.577%	$52.2357	$52.24	$52.25	$52.20
Purchase #4	$136.59	5.630%	$144.28	$144.28	$144.30	$144.30
Purchase #5	$90.99	10.618%	$100.6513	$100.65	$100.65	$100.70
Purchase #6	$207.89	3.649%	$215.4759	$215.48	$215.50	$215.50
Purchase #7	$234.33	10.658%	$259.3049	$259.30	$259.30	$259.30
7 purchase totals =	$944.24		$1,009.0264	$1,009.03	$1,009.05	$1,009.10