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	$248.98	9.778%	$273.3253	$273.33	$273.35	$273.30
Purchase #2	$102.52	8.297%	$111.0261	$111.03	$111.05	$111.00
Purchase #3	$111.30	3.746%	$115.4693	$115.47	$115.45	$115.50
Purchase #4	$50.35	6.826%	$53.7869	$53.79	$53.80	$53.80
Purchase #5	$245.41	13.224%	$277.863	$277.86	$277.85	$277.90
Purchase #6	$153.81	13.410%	$174.4359	$174.44	$174.45	$174.40
Purchase #7	$75.93	12.853%	$85.6893	$85.69	$85.70	$85.70
7 purchase totals =	$988.30		$1,091.5958	$1,091.61	$1,091.65	$1,091.60