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	$158.87	13.454%	$180.2444	$180.24	$180.25	$180.20
Purchase #2	$106.97	5.502%	$112.8555	$112.86	$112.85	$112.90
Purchase #3	$133.43	6.733%	$142.4138	$142.41	$142.40	$142.40
Purchase #4	$56.87	5.768%	$60.1503	$60.15	$60.15	$60.20
Purchase #5	$99.48	12.720%	$112.1339	$112.13	$112.15	$112.10
Purchase #6	$196.28	13.392%	$222.5658	$222.57	$222.55	$222.60
Purchase #7	$19.59	6.871%	$20.936	$20.94	$20.95	$20.90
7 purchase totals =	$771.49		$851.2997	$851.30	$851.30	$851.30