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	$9.94	5.179%	$10.4548	$10.45	$10.45	$10.50
Purchase #2	$163.49	13.617%	$185.7524	$185.75	$185.75	$185.80
Purchase #3	$155.72	8.756%	$169.3548	$169.35	$169.35	$169.40
Purchase #4	$109.74	9.128%	$119.7571	$119.76	$119.75	$119.80
Purchase #5	$28.39	11.288%	$31.5947	$31.59	$31.60	$31.60
Purchase #6	$120.91	6.444%	$128.7014	$128.70	$128.70	$128.70
Purchase #7	$81.35	5.822%	$86.0862	$86.09	$86.10	$86.10
7 purchase totals =	$669.54		$731.7014	$731.69	$731.70	$731.90