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	$136.65	5.409%	$144.0414	$144.04	$144.05	$144.00
Purchase #2	$82.49	4.145%	$85.9092	$85.91	$85.90	$85.90
Purchase #3	$96.60	6.228%	$102.6162	$102.62	$102.60	$102.60
Purchase #4	$131.93	12.356%	$148.2313	$148.23	$148.25	$148.20
Purchase #5	$63.63	12.697%	$71.7091	$71.71	$71.70	$71.70
Purchase #6	$98.46	6.690%	$105.047	$105.05	$105.05	$105.00
Purchase #7	$103.66	7.233%	$111.1577	$111.16	$111.15	$111.20
7 purchase totals =	$713.42		$768.7119	$768.72	$768.70	$768.60