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	$242.27	5.387%	$255.3211	$255.32	$255.30	$255.30
Purchase #2	$114.94	4.726%	$120.3721	$120.37	$120.35	$120.40
Purchase #3	$117.63	7.115%	$125.9994	$126.00	$126.00	$126.00
Purchase #4	$87.31	9.809%	$95.8742	$95.87	$95.85	$95.90
Purchase #5	$127.54	3.146%	$131.5524	$131.55	$131.55	$131.60
Purchase #6	$44.40	5.642%	$46.905	$46.91	$46.90	$46.90
Purchase #7	$137.54	7.519%	$147.8816	$147.88	$147.90	$147.90
7 purchase totals =	$871.63		$923.9058	$923.90	$923.85	$924.00