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	$167.96	6.841%	$179.4501	$179.45	$179.45	$179.50
Purchase #2	$55.90	9.242%	$61.0663	$61.07	$61.05	$61.10
Purchase #3	$43.33	7.288%	$46.4879	$46.49	$46.50	$46.50
Purchase #4	$63.36	5.681%	$66.9595	$66.96	$66.95	$67.00
Purchase #5	$77.87	8.687%	$84.6346	$84.63	$84.65	$84.60
Purchase #6	$182.48	6.606%	$194.5346	$194.53	$194.55	$194.50
Purchase #7	$33.56	3.262%	$34.6547	$34.65	$34.65	$34.70
7 purchase totals =	$624.46		$667.7877	$667.78	$667.80	$667.90