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	$16.31	3.475%	$16.8768	$16.88	$16.90	$16.90
Purchase #2	$56.95	11.525%	$63.5135	$63.51	$63.50	$63.50
Purchase #3	$201.84	3.154%	$208.206	$208.21	$208.20	$208.20
Purchase #4	$61.30	10.634%	$67.8186	$67.82	$67.80	$67.80
Purchase #5	$46.77	12.503%	$52.6177	$52.62	$52.60	$52.60
Purchase #6	$52.40	9.804%	$57.5373	$57.54	$57.55	$57.50
Purchase #7	$78.34	5.286%	$82.4811	$82.48	$82.50	$82.50
7 purchase totals =	$513.91		$549.0510	$549.06	$549.05	$549.00