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	$118.52	12.143%	$132.9119	$132.91	$132.90	$132.90
Purchase #2	$185.36	9.834%	$203.5883	$203.59	$203.60	$203.60
Purchase #3	$18.39	11.248%	$20.4585	$20.46	$20.45	$20.50
Purchase #4	$195.99	13.857%	$223.1483	$223.15	$223.15	$223.10
Purchase #5	$248.78	8.514%	$269.9611	$269.96	$269.95	$270.00
Purchase #6	$156.33	8.410%	$169.4774	$169.48	$169.50	$169.50
Purchase #7	$88.85	13.162%	$100.5444	$100.54	$100.55	$100.50
7 purchase totals =	$1,012.22		$1,120.0899	$1,120.09	$1,120.10	$1,120.10