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	$90.48	11.154%	$100.5721	$100.57	$100.55	$100.60
Purchase #2	$209.50	6.627%	$223.3836	$223.38	$223.40	$223.40
Purchase #3	$240.91	3.608%	$249.602	$249.60	$249.60	$249.60
Purchase #4	$10.25	7.637%	$11.0328	$11.03	$11.05	$11.00
Purchase #5	$60.31	8.374%	$65.3604	$65.36	$65.35	$65.40
Purchase #6	$43.56	4.746%	$45.6274	$45.63	$45.65	$45.60
Purchase #7	$18.32	13.691%	$20.8282	$20.83	$20.85	$20.80
7 purchase totals =	$673.33		$716.4065	$716.40	$716.45	$716.40