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	$249.59	12.428%	$280.609	$280.61	$280.60	$280.60
Purchase #2	$64.31	4.362%	$67.1152	$67.12	$67.10	$67.10
Purchase #3	$215.53	7.562%	$231.8284	$231.83	$231.85	$231.80
Purchase #4	$52.87	8.158%	$57.1831	$57.18	$57.20	$57.20
Purchase #5	$201.95	10.354%	$222.8599	$222.86	$222.85	$222.90
Purchase #6	$234.95	6.467%	$250.1442	$250.14	$250.15	$250.10
Purchase #7	$135.81	10.823%	$150.5087	$150.51	$150.50	$150.50
7 purchase totals =	$1,155.01		$1,260.2485	$1,260.25	$1,260.25	$1,260.20