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	$63.47	4.832%	$66.5369	$66.54	$66.55	$66.50
Purchase #2	$218.92	9.814%	$240.4048	$240.40	$240.40	$240.40
Purchase #3	$167.69	6.366%	$178.3651	$178.37	$178.35	$178.40
Purchase #4	$101.82	3.721%	$105.6087	$105.61	$105.60	$105.60
Purchase #5	$100.78	7.124%	$107.9596	$107.96	$107.95	$108.00
Purchase #6	$25.30	8.812%	$27.5294	$27.53	$27.55	$27.50
Purchase #7	$156.84	13.843%	$178.5514	$178.55	$178.55	$178.60
7 purchase totals =	$834.82		$904.9559	$904.96	$904.95	$905.00