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	$139.54	7.869%	$150.5204	$150.52	$150.50	$150.50
Purchase #2	$177.92	5.360%	$187.4565	$187.46	$187.45	$187.50
Purchase #3	$152.25	4.576%	$159.217	$159.22	$159.20	$159.20
Purchase #4	$162.52	12.513%	$182.8561	$182.86	$182.85	$182.90
Purchase #5	$125.71	6.706%	$134.1401	$134.14	$134.15	$134.10
Purchase #6	$25.46	12.115%	$28.5445	$28.54	$28.55	$28.50
Purchase #7	$151.62	5.585%	$160.088	$160.09	$160.10	$160.10
7 purchase totals =	$935.02		$1,002.8226	$1,002.83	$1,002.80	$1,002.80