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	$135.44	5.580%	$142.9976	$143.00	$143.00	$143.00
Purchase #2	$250.34	7.622%	$269.4209	$269.42	$269.40	$269.40
Purchase #3	$53.45	4.814%	$56.0231	$56.02	$56.00	$56.00
Purchase #4	$97.82	6.855%	$104.5256	$104.53	$104.55	$104.50
Purchase #5	$78.32	6.457%	$83.3771	$83.38	$83.40	$83.40
Purchase #6	$218.29	7.377%	$234.3933	$234.39	$234.40	$234.40
Purchase #7	$38.95	8.243%	$42.1606	$42.16	$42.15	$42.20
7 purchase totals =	$872.61		$932.8982	$932.90	$932.90	$932.90