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	$27.52	7.859%	$29.6828	$29.68	$29.70	$29.70
Purchase #2	$236.63	9.843%	$259.9215	$259.92	$259.90	$259.90
Purchase #3	$19.35	6.406%	$20.5896	$20.59	$20.60	$20.60
Purchase #4	$86.34	8.349%	$93.5485	$93.55	$93.55	$93.50
Purchase #5	$145.50	3.424%	$150.4819	$150.48	$150.50	$150.50
Purchase #6	$68.61	3.560%	$71.0525	$71.05	$71.05	$71.10
Purchase #7	$55.41	8.199%	$59.9531	$59.95	$59.95	$60.00
7 purchase totals =	$639.36		$685.2299	$685.22	$685.25	$685.30