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	$59.34	8.630%	$64.461	$64.46	$64.45	$64.50
Purchase #2	$140.47	4.322%	$146.5411	$146.54	$146.55	$146.50
Purchase #3	$80.71	11.299%	$89.8294	$89.83	$89.85	$89.80
Purchase #4	$173.39	11.654%	$193.5969	$193.60	$193.60	$193.60
Purchase #5	$229.32	3.662%	$237.7177	$237.72	$237.70	$237.70
Purchase #6	$174.92	5.463%	$184.4759	$184.48	$184.50	$184.50
Purchase #7	$157.46	7.593%	$169.4159	$169.42	$169.40	$169.40
7 purchase totals =	$1,015.61		$1,086.0379	$1,086.05	$1,086.05	$1,086.00