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	$224.63	13.752%	$255.5211	$255.52	$255.50	$255.50
Purchase #2	$86.80	3.160%	$89.5429	$89.54	$89.55	$89.50
Purchase #3	$154.40	5.821%	$163.3876	$163.39	$163.40	$163.40
Purchase #4	$151.42	8.746%	$164.6632	$164.66	$164.65	$164.70
Purchase #5	$74.85	7.338%	$80.3425	$80.34	$80.35	$80.30
Purchase #6	$209.28	7.525%	$225.0283	$225.03	$225.05	$225.00
Purchase #7	$88.52	5.414%	$93.3125	$93.31	$93.30	$93.30
7 purchase totals =	$989.90		$1,071.7981	$1,071.79	$1,071.80	$1,071.70