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	$240.30	10.381%	$265.2455	$265.25	$265.25	$265.20
Purchase #2	$147.70	11.605%	$164.8406	$164.84	$164.85	$164.80
Purchase #3	$109.71	12.197%	$123.0913	$123.09	$123.10	$123.10
Purchase #4	$168.87	13.507%	$191.6793	$191.68	$191.70	$191.70
Purchase #5	$92.78	12.414%	$104.2977	$104.30	$104.30	$104.30
Purchase #6	$96.84	7.136%	$103.7505	$103.75	$103.75	$103.80
Purchase #7	$164.73	8.248%	$178.3169	$178.32	$178.30	$178.30
7 purchase totals =	$1,020.93		$1,131.2218	$1,131.23	$1,131.25	$1,131.20