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	$20.73	13.599%	$23.5491	$23.55	$23.55	$23.50
Purchase #2	$52.61	12.808%	$59.3483	$59.35	$59.35	$59.30
Purchase #3	$113.73	8.440%	$123.3288	$123.33	$123.35	$123.30
Purchase #4	$58.84	9.109%	$64.1997	$64.20	$64.20	$64.20
Purchase #5	$77.83	12.764%	$87.7642	$87.76	$87.75	$87.80
Purchase #6	$163.29	11.764%	$182.4994	$182.50	$182.50	$182.50
Purchase #7	$176.81	10.797%	$195.9002	$195.90	$195.90	$195.90
7 purchase totals =	$663.84		$736.5897	$736.59	$736.60	$736.50