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	$75.53	6.766%	$80.6404	$80.64	$80.65	$80.60
Purchase #2	$24.69	3.126%	$25.4618	$25.46	$25.45	$25.50
Purchase #3	$243.99	6.335%	$259.4468	$259.45	$259.45	$259.40
Purchase #4	$103.81	7.449%	$111.5428	$111.54	$111.55	$111.50
Purchase #5	$163.83	11.566%	$182.7786	$182.78	$182.80	$182.80
Purchase #6	$194.40	11.212%	$216.1961	$216.20	$216.20	$216.20
Purchase #7	$88.60	13.777%	$100.8064	$100.81	$100.80	$100.80
7 purchase totals =	$894.85		$976.8729	$976.88	$976.90	$976.80