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	$123.97	3.761%	$128.6325	$128.63	$128.65	$128.60
Purchase #2	$13.94	3.467%	$14.4233	$14.42	$14.40	$14.40
Purchase #3	$75.72	8.864%	$82.4318	$82.43	$82.45	$82.40
Purchase #4	$105.38	8.583%	$114.4248	$114.42	$114.40	$114.40
Purchase #5	$221.25	13.215%	$250.4882	$250.49	$250.50	$250.50
Purchase #6	$39.26	4.365%	$40.9737	$40.97	$40.95	$41.00
Purchase #7	$161.78	10.365%	$178.5485	$178.55	$178.55	$178.50
7 purchase totals =	$741.30		$809.9228	$809.91	$809.90	$809.80