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	$55.78	3.524%	$57.7457	$57.75	$57.75	$57.70
Purchase #2	$148.28	7.525%	$159.4381	$159.44	$159.45	$159.40
Purchase #3	$208.53	3.789%	$216.4312	$216.43	$216.45	$216.40
Purchase #4	$56.47	5.696%	$59.6865	$59.69	$59.70	$59.70
Purchase #5	$137.79	4.665%	$144.2179	$144.22	$144.20	$144.20
Purchase #6	$142.28	5.736%	$150.4412	$150.44	$150.45	$150.40
Purchase #7	$117.61	12.695%	$132.5406	$132.54	$132.55	$132.50
7 purchase totals =	$866.74		$920.5012	$920.51	$920.55	$920.30