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	$126.75	13.775%	$144.2098	$144.21	$144.20	$144.20
Purchase #2	$207.84	6.590%	$221.5367	$221.54	$221.55	$221.50
Purchase #3	$29.83	7.831%	$32.166	$32.17	$32.15	$32.20
Purchase #4	$71.98	8.465%	$78.0731	$78.07	$78.05	$78.10
Purchase #5	$95.38	7.732%	$102.7548	$102.75	$102.75	$102.80
Purchase #6	$91.54	7.587%	$98.4851	$98.49	$98.50	$98.50
Purchase #7	$88.53	9.105%	$96.5907	$96.59	$96.60	$96.60
7 purchase totals =	$711.85		$773.8162	$773.82	$773.80	$773.90