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	$171.26	4.524%	$179.0078	$179.01	$179.00	$179.00
Purchase #2	$31.31	7.115%	$33.5377	$33.54	$33.55	$33.50
Purchase #3	$140.25	4.482%	$146.536	$146.54	$146.55	$146.50
Purchase #4	$25.33	8.184%	$27.403	$27.40	$27.40	$27.40
Purchase #5	$110.41	7.267%	$118.4335	$118.43	$118.45	$118.40
Purchase #6	$29.93	8.634%	$32.5142	$32.51	$32.50	$32.50
Purchase #7	$239.74	9.513%	$262.5465	$262.55	$262.55	$262.50
7 purchase totals =	$748.23		$799.9787	$799.98	$800.00	$799.80