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	$128.32	6.544%	$136.7173	$136.72	$136.70	$136.70
Purchase #2	$201.71	9.214%	$220.2956	$220.30	$220.30	$220.30
Purchase #3	$231.69	10.789%	$256.687	$256.69	$256.70	$256.70
Purchase #4	$69.82	9.719%	$76.6058	$76.61	$76.60	$76.60
Purchase #5	$69.33	13.278%	$78.5356	$78.54	$78.55	$78.50
Purchase #6	$94.39	8.116%	$102.0507	$102.05	$102.05	$102.10
Purchase #7	$36.29	3.295%	$37.4858	$37.49	$37.50	$37.50
7 purchase totals =	$831.55		$908.3778	$908.40	$908.40	$908.40