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	$125.96	10.432%	$139.1001	$139.10	$139.10	$139.10
Purchase #2	$161.51	3.689%	$167.4681	$167.47	$167.45	$167.50
Purchase #3	$99.40	9.718%	$109.0597	$109.06	$109.05	$109.10
Purchase #4	$189.72	6.339%	$201.7464	$201.75	$201.75	$201.70
Purchase #5	$121.97	4.183%	$127.072	$127.07	$127.05	$127.10
Purchase #6	$245.48	12.389%	$275.8925	$275.89	$275.90	$275.90
Purchase #7	$233.86	12.704%	$263.5696	$263.57	$263.55	$263.60
7 purchase totals =	$1,177.90		$1,283.9084	$1,283.91	$1,283.85	$1,284.00