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	$180.79	4.328%	$188.6146	$188.61	$188.60	$188.60
Purchase #2	$151.26	13.567%	$171.7814	$171.78	$171.80	$171.80
Purchase #3	$139.53	6.458%	$148.5408	$148.54	$148.55	$148.50
Purchase #4	$67.66	6.640%	$72.1526	$72.15	$72.15	$72.20
Purchase #5	$106.94	5.583%	$112.9105	$112.91	$112.90	$112.90
Purchase #6	$151.89	10.256%	$167.4678	$167.47	$167.45	$167.50
Purchase #7	$51.30	9.513%	$56.1802	$56.18	$56.20	$56.20
7 purchase totals =	$849.37		$917.6479	$917.64	$917.65	$917.70