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	$145.52	4.314%	$151.7977	$151.80	$151.80	$151.80
Purchase #2	$236.57	10.548%	$261.5234	$261.52	$261.50	$261.50
Purchase #3	$83.89	6.240%	$89.1247	$89.12	$89.10	$89.10
Purchase #4	$77.98	9.501%	$85.3889	$85.39	$85.40	$85.40
Purchase #5	$61.86	12.262%	$69.4453	$69.45	$69.45	$69.40
Purchase #6	$213.56	11.206%	$237.4915	$237.49	$237.50	$237.50
Purchase #7	$196.90	10.750%	$218.0668	$218.07	$218.05	$218.10
7 purchase totals =	$1,016.28		$1,112.8383	$1,112.84	$1,112.80	$1,112.80