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	$21.53	7.364%	$23.1155	$23.12	$23.10	$23.10
Purchase #2	$125.84	6.254%	$133.71	$133.71	$133.70	$133.70
Purchase #3	$105.64	5.628%	$111.5854	$111.59	$111.60	$111.60
Purchase #4	$78.79	12.186%	$88.3913	$88.39	$88.40	$88.40
Purchase #5	$187.82	8.252%	$203.3189	$203.32	$203.30	$203.30
Purchase #6	$78.46	4.334%	$81.8605	$81.86	$81.85	$81.90
Purchase #7	$133.70	4.356%	$139.524	$139.52	$139.50	$139.50
7 purchase totals =	$731.78		$781.5056	$781.51	$781.45	$781.50