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	$150.42	11.661%	$167.9605	$167.96	$167.95	$168.00
Purchase #2	$134.72	11.665%	$150.4351	$150.44	$150.45	$150.40
Purchase #3	$89.46	7.497%	$96.1668	$96.17	$96.15	$96.20
Purchase #4	$172.33	12.614%	$194.0677	$194.07	$194.05	$194.10
Purchase #5	$146.36	5.821%	$154.8796	$154.88	$154.90	$154.90
Purchase #6	$29.86	12.448%	$33.577	$33.58	$33.60	$33.60
Purchase #7	$168.25	8.204%	$182.0532	$182.05	$182.05	$182.10
7 purchase totals =	$891.40		$979.1399	$979.15	$979.15	$979.30