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	$173.93	6.396%	$185.0546	$185.05	$185.05	$185.10
Purchase #2	$83.33	7.616%	$89.6764	$89.68	$89.70	$89.70
Purchase #3	$58.77	6.436%	$62.5524	$62.55	$62.55	$62.60
Purchase #4	$117.51	6.110%	$124.6899	$124.69	$124.70	$124.70
Purchase #5	$168.70	11.357%	$187.8593	$187.86	$187.85	$187.90
Purchase #6	$81.87	11.505%	$91.2891	$91.29	$91.30	$91.30
Purchase #7	$176.78	11.522%	$197.1486	$197.15	$197.15	$197.10
7 purchase totals =	$860.89		$938.2703	$938.27	$938.30	$938.40