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	$226.28	5.871%	$239.5649	$239.56	$239.55	$239.60
Purchase #2	$142.70	5.383%	$150.3815	$150.38	$150.40	$150.40
Purchase #3	$243.90	4.797%	$255.5999	$255.60	$255.60	$255.60
Purchase #4	$68.63	4.478%	$71.7033	$71.70	$71.70	$71.70
Purchase #5	$118.34	11.313%	$131.7278	$131.73	$131.75	$131.70
Purchase #6	$196.91	9.477%	$215.5712	$215.57	$215.55	$215.60
Purchase #7	$27.42	4.723%	$28.715	$28.72	$28.70	$28.70
7 purchase totals =	$1,024.18		$1,093.2636	$1,093.26	$1,093.25	$1,093.30