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	$177.88	6.586%	$189.5952	$189.60	$189.60	$189.60
Purchase #2	$40.69	9.180%	$44.4253	$44.43	$44.45	$44.40
Purchase #3	$208.42	4.856%	$218.5409	$218.54	$218.55	$218.50
Purchase #4	$174.41	12.608%	$196.3996	$196.40	$196.40	$196.40
Purchase #5	$139.54	12.231%	$156.6071	$156.61	$156.60	$156.60
Purchase #6	$34.38	6.261%	$36.5325	$36.53	$36.55	$36.50
Purchase #7	$147.64	13.467%	$167.5227	$167.52	$167.50	$167.50
7 purchase totals =	$922.96		$1,009.6233	$1,009.63	$1,009.65	$1,009.50