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	$183.84	13.572%	$208.7908	$208.79	$208.80	$208.80
Purchase #2	$31.85	4.663%	$33.3352	$33.34	$33.35	$33.30
Purchase #3	$45.27	13.586%	$51.4204	$51.42	$51.40	$51.40
Purchase #4	$112.73	12.504%	$126.8258	$126.83	$126.85	$126.80
Purchase #5	$63.61	12.354%	$71.4684	$71.47	$71.45	$71.50
Purchase #6	$70.35	9.731%	$77.1958	$77.20	$77.20	$77.20
Purchase #7	$103.96	5.362%	$109.5343	$109.53	$109.55	$109.50
7 purchase totals =	$611.61		$678.5707	$678.58	$678.60	$678.50