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	$100.65	11.652%	$112.3777	$112.38	$112.40	$112.40
Purchase #2	$127.80	6.654%	$136.3038	$136.30	$136.30	$136.30
Purchase #3	$168.83	5.704%	$178.4601	$178.46	$178.45	$178.50
Purchase #4	$165.63	3.450%	$171.3442	$171.34	$171.35	$171.30
Purchase #5	$105.79	13.344%	$119.9066	$119.91	$119.90	$119.90
Purchase #6	$220.44	7.380%	$236.7085	$236.71	$236.70	$236.70
Purchase #7	$118.70	8.212%	$128.4476	$128.45	$128.45	$128.40
7 purchase totals =	$1,007.84		$1,083.5485	$1,083.55	$1,083.55	$1,083.50