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	$228.61	13.653%	$259.8221	$259.82	$259.80	$259.80
Purchase #2	$80.51	6.377%	$85.6441	$85.64	$85.65	$85.60
Purchase #3	$60.27	8.661%	$65.49	$65.49	$65.50	$65.50
Purchase #4	$160.78	4.423%	$167.8913	$167.89	$167.90	$167.90
Purchase #5	$35.45	9.488%	$38.8135	$38.81	$38.80	$38.80
Purchase #6	$145.42	3.404%	$150.3701	$150.37	$150.35	$150.40
Purchase #7	$179.26	6.193%	$190.3616	$190.36	$190.35	$190.40
7 purchase totals =	$890.30		$958.3927	$958.38	$958.35	$958.40