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	$177.97	12.531%	$200.2714	$200.27	$200.25	$200.30
Purchase #2	$12.57	12.223%	$14.1064	$14.11	$14.10	$14.10
Purchase #3	$168.54	11.118%	$187.2783	$187.28	$187.30	$187.30
Purchase #4	$18.71	11.434%	$20.8493	$20.85	$20.85	$20.80
Purchase #5	$154.47	10.725%	$171.0369	$171.04	$171.05	$171.00
Purchase #6	$185.44	8.256%	$200.7499	$200.75	$200.75	$200.70
Purchase #7	$185.45	7.150%	$198.7097	$198.71	$198.70	$198.70
7 purchase totals =	$903.15		$993.0019	$993.01	$993.00	$992.90