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	$243.93	12.204%	$273.6992	$273.70	$273.70	$273.70
Purchase #2	$25.36	9.462%	$27.7596	$27.76	$27.75	$27.80
Purchase #3	$67.80	7.186%	$72.6721	$72.67	$72.65	$72.70
Purchase #4	$37.72	7.757%	$40.6459	$40.65	$40.65	$40.60
Purchase #5	$60.45	12.246%	$67.8527	$67.85	$67.85	$67.90
Purchase #6	$57.29	4.304%	$59.7558	$59.76	$59.75	$59.80
Purchase #7	$134.86	8.870%	$146.8221	$146.82	$146.80	$146.80
7 purchase totals =	$627.41		$689.2074	$689.21	$689.15	$689.30