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	$15.50	13.582%	$17.6052	$17.61	$17.60	$17.60
Purchase #2	$88.66	6.590%	$94.5027	$94.50	$94.50	$94.50
Purchase #3	$67.87	11.328%	$75.5583	$75.56	$75.55	$75.60
Purchase #4	$73.57	6.411%	$78.2866	$78.29	$78.30	$78.30
Purchase #5	$113.76	6.109%	$120.7096	$120.71	$120.70	$120.70
Purchase #6	$59.38	11.764%	$66.3655	$66.37	$66.35	$66.40
Purchase #7	$165.85	12.670%	$186.8632	$186.86	$186.85	$186.90
7 purchase totals =	$584.59		$639.8911	$639.90	$639.85	$640.00