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	$110.55	11.395%	$123.1472	$123.15	$123.15	$123.10
Purchase #2	$112.63	12.592%	$126.8124	$126.81	$126.80	$126.80
Purchase #3	$136.88	13.757%	$155.7106	$155.71	$155.70	$155.70
Purchase #4	$161.33	7.662%	$173.6911	$173.69	$173.70	$173.70
Purchase #5	$216.91	12.242%	$243.4641	$243.46	$243.45	$243.50
Purchase #6	$94.35	12.219%	$105.8786	$105.88	$105.90	$105.90
Purchase #7	$243.89	9.145%	$266.1937	$266.19	$266.20	$266.20
7 purchase totals =	$1,076.54		$1,194.8977	$1,194.89	$1,194.90	$1,194.90