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	$178.27	6.282%	$189.4689	$189.47	$189.45	$189.50
Purchase #2	$99.94	12.551%	$112.4835	$112.48	$112.50	$112.50
Purchase #3	$47.70	8.192%	$51.6076	$51.61	$51.60	$51.60
Purchase #4	$235.67	12.642%	$265.4634	$265.46	$265.45	$265.50
Purchase #5	$141.44	10.319%	$156.0352	$156.04	$156.05	$156.00
Purchase #6	$97.84	13.481%	$111.0298	$111.03	$111.05	$111.00
Purchase #7	$223.88	3.246%	$231.1471	$231.15	$231.15	$231.10
7 purchase totals =	$1,024.74		$1,117.2355	$1,117.24	$1,117.25	$1,117.20