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	$160.30	5.802%	$169.6006	$169.60	$169.60	$169.60
Purchase #2	$169.38	6.566%	$180.5015	$180.50	$180.50	$180.50
Purchase #3	$178.34	10.216%	$196.5592	$196.56	$196.55	$196.60
Purchase #4	$231.30	6.203%	$245.6475	$245.65	$245.65	$245.60
Purchase #5	$108.79	3.607%	$112.7141	$112.71	$112.70	$112.70
Purchase #6	$112.32	6.284%	$119.3782	$119.38	$119.40	$119.40
Purchase #7	$204.96	13.209%	$232.0332	$232.03	$232.05	$232.00
7 purchase totals =	$1,165.39		$1,256.4343	$1,256.43	$1,256.45	$1,256.40