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	$153.89	5.331%	$162.0939	$162.09	$162.10	$162.10
Purchase #2	$44.67	11.700%	$49.8964	$49.90	$49.90	$49.90
Purchase #3	$71.35	9.654%	$78.2381	$78.24	$78.25	$78.20
Purchase #4	$171.71	8.164%	$185.7284	$185.73	$185.75	$185.70
Purchase #5	$62.70	13.429%	$71.12	$71.12	$71.10	$71.10
Purchase #6	$231.78	11.138%	$257.5957	$257.60	$257.60	$257.60
Purchase #7	$22.93	9.793%	$25.1755	$25.18	$25.20	$25.20
7 purchase totals =	$759.03		$829.8480	$829.86	$829.90	$829.80