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	$29.90	7.157%	$32.0399	$32.04	$32.05	$32.00
Purchase #2	$152.55	10.726%	$168.9125	$168.91	$168.90	$168.90
Purchase #3	$165.71	6.715%	$176.8374	$176.84	$176.85	$176.80
Purchase #4	$112.45	10.224%	$123.9469	$123.95	$123.95	$123.90
Purchase #5	$131.65	6.170%	$139.7728	$139.77	$139.75	$139.80
Purchase #6	$103.36	11.148%	$114.8826	$114.88	$114.90	$114.90
Purchase #7	$135.87	4.369%	$141.8062	$141.81	$141.80	$141.80
7 purchase totals =	$831.49		$898.1983	$898.20	$898.20	$898.10