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	$45.82	9.678%	$50.2545	$50.25	$50.25	$50.30
Purchase #2	$188.72	6.268%	$200.549	$200.55	$200.55	$200.50
Purchase #3	$199.56	11.872%	$223.2518	$223.25	$223.25	$223.30
Purchase #4	$198.70	12.637%	$223.8097	$223.81	$223.80	$223.80
Purchase #5	$165.29	7.360%	$177.4553	$177.46	$177.45	$177.50
Purchase #6	$113.60	13.325%	$128.7372	$128.74	$128.75	$128.70
Purchase #7	$228.89	4.706%	$239.6616	$239.66	$239.65	$239.70
7 purchase totals =	$1,140.58		$1,243.7191	$1,243.72	$1,243.70	$1,243.80