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	$229.72	12.486%	$258.4028	$258.40	$258.40	$258.40
Purchase #2	$30.73	9.861%	$33.7603	$33.76	$33.75	$33.80
Purchase #3	$136.25	11.431%	$151.8247	$151.82	$151.80	$151.80
Purchase #4	$169.72	3.637%	$175.8927	$175.89	$175.90	$175.90
Purchase #5	$109.75	8.686%	$119.2829	$119.28	$119.30	$119.30
Purchase #6	$87.91	8.393%	$95.2883	$95.29	$95.30	$95.30
Purchase #7	$97.63	11.660%	$109.0137	$109.01	$109.00	$109.00
7 purchase totals =	$861.71		$943.4654	$943.45	$943.45	$943.50