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	$104.87	9.187%	$114.5044	$114.50	$114.50	$114.50
Purchase #2	$40.82	6.696%	$43.5533	$43.55	$43.55	$43.60
Purchase #3	$111.63	10.733%	$123.6112	$123.61	$123.60	$123.60
Purchase #4	$100.90	7.386%	$108.3525	$108.35	$108.35	$108.40
Purchase #5	$128.42	9.624%	$140.7791	$140.78	$140.80	$140.80
Purchase #6	$70.33	12.331%	$79.0024	$79.00	$79.00	$79.00
Purchase #7	$48.73	13.772%	$55.4411	$55.44	$55.45	$55.40
7 purchase totals =	$605.70		$665.2440	$665.23	$665.25	$665.30