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	$40.97	3.223%	$42.2905	$42.29	$42.30	$42.30
Purchase #2	$7.31	6.614%	$7.7935	$7.79	$7.80	$7.80
Purchase #3	$164.55	11.851%	$184.0508	$184.05	$184.05	$184.10
Purchase #4	$31.31	4.385%	$32.6829	$32.68	$32.70	$32.70
Purchase #5	$152.53	7.583%	$164.0963	$164.10	$164.10	$164.10
Purchase #6	$151.27	6.277%	$160.7652	$160.77	$160.75	$160.80
Purchase #7	$141.56	7.628%	$152.3582	$152.36	$152.35	$152.40
7 purchase totals =	$689.50		$744.0374	$744.04	$744.05	$744.20