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	$127.95	8.796%	$139.2045	$139.20	$139.20	$139.20
Purchase #2	$82.55	7.659%	$88.8725	$88.87	$88.85	$88.90
Purchase #3	$103.95	7.262%	$111.4988	$111.50	$111.50	$111.50
Purchase #4	$80.29	13.286%	$90.9573	$90.96	$90.95	$91.00
Purchase #5	$221.55	10.223%	$244.1991	$244.20	$244.20	$244.20
Purchase #6	$195.33	13.494%	$221.6878	$221.69	$221.70	$221.70
Purchase #7	$35.93	12.639%	$40.4712	$40.47	$40.45	$40.50
7 purchase totals =	$847.55		$936.8912	$936.89	$936.85	$937.00