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	$96.43	13.438%	$109.3883	$109.39	$109.40	$109.40
Purchase #2	$151.46	12.742%	$170.759	$170.76	$170.75	$170.80
Purchase #3	$156.71	8.239%	$169.6213	$169.62	$169.60	$169.60
Purchase #4	$185.87	6.856%	$198.6132	$198.61	$198.60	$198.60
Purchase #5	$65.46	3.347%	$67.6509	$67.65	$67.65	$67.70
Purchase #6	$206.52	10.561%	$228.3306	$228.33	$228.35	$228.30
Purchase #7	$138.46	6.214%	$147.0639	$147.06	$147.05	$147.10
7 purchase totals =	$1,000.91		$1,091.4272	$1,091.42	$1,091.40	$1,091.50