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	$123.67	10.269%	$136.3697	$136.37	$136.35	$136.40
Purchase #2	$48.45	6.812%	$51.7504	$51.75	$51.75	$51.80
Purchase #3	$96.55	13.571%	$109.6528	$109.65	$109.65	$109.70
Purchase #4	$131.78	5.407%	$138.9053	$138.91	$138.90	$138.90
Purchase #5	$221.93	12.864%	$250.4791	$250.48	$250.50	$250.50
Purchase #6	$123.76	4.171%	$128.922	$128.92	$128.90	$128.90
Purchase #7	$78.92	3.765%	$81.8913	$81.89	$81.90	$81.90
7 purchase totals =	$825.06		$897.9706	$897.97	$897.95	$898.10