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	$80.83	10.820%	$89.5758	$89.58	$89.60	$89.60
Purchase #2	$220.48	7.581%	$237.1946	$237.19	$237.20	$237.20
Purchase #3	$82.39	7.723%	$88.753	$88.75	$88.75	$88.80
Purchase #4	$61.72	7.544%	$66.3762	$66.38	$66.40	$66.40
Purchase #5	$250.46	9.168%	$273.4222	$273.42	$273.40	$273.40
Purchase #6	$67.41	5.800%	$71.3198	$71.32	$71.30	$71.30
Purchase #7	$24.90	13.228%	$28.1938	$28.19	$28.20	$28.20
7 purchase totals =	$788.19		$854.8354	$854.83	$854.85	$854.90