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	$234.78	9.373%	$256.7859	$256.79	$256.80	$256.80
Purchase #2	$112.52	13.619%	$127.8441	$127.84	$127.85	$127.80
Purchase #3	$126.52	12.116%	$141.8492	$141.85	$141.85	$141.80
Purchase #4	$206.88	5.578%	$218.4198	$218.42	$218.40	$218.40
Purchase #5	$245.28	7.408%	$263.4503	$263.45	$263.45	$263.50
Purchase #6	$178.90	13.786%	$203.5632	$203.56	$203.55	$203.60
Purchase #7	$203.43	9.585%	$222.9288	$222.93	$222.95	$222.90
7 purchase totals =	$1,308.31		$1,434.8413	$1,434.84	$1,434.85	$1,434.80