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	$52.69	12.864%	$59.468	$59.47	$59.45	$59.50
Purchase #2	$144.42	6.315%	$153.5401	$153.54	$153.55	$153.50
Purchase #3	$193.54	3.819%	$200.9313	$200.93	$200.95	$200.90
Purchase #4	$47.35	10.577%	$52.3582	$52.36	$52.35	$52.40
Purchase #5	$109.62	6.128%	$116.3375	$116.34	$116.35	$116.30
Purchase #6	$98.79	4.692%	$103.4252	$103.43	$103.45	$103.40
Purchase #7	$146.39	8.230%	$158.4379	$158.44	$158.45	$158.40
7 purchase totals =	$792.80		$844.4982	$844.51	$844.55	$844.40