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	$88.57	13.364%	$100.4065	$100.41	$100.40	$100.40
Purchase #2	$186.87	10.364%	$206.2372	$206.24	$206.25	$206.20
Purchase #3	$141.76	11.685%	$158.3247	$158.32	$158.30	$158.30
Purchase #4	$114.89	3.858%	$119.3225	$119.32	$119.30	$119.30
Purchase #5	$233.46	12.256%	$262.0729	$262.07	$262.05	$262.10
Purchase #6	$204.46	11.441%	$227.8523	$227.85	$227.85	$227.90
Purchase #7	$120.61	11.384%	$134.3402	$134.34	$134.35	$134.30
7 purchase totals =	$1,090.62		$1,208.5563	$1,208.55	$1,208.50	$1,208.50