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	$245.66	13.605%	$279.082	$279.08	$279.10	$279.10
Purchase #2	$206.81	8.529%	$224.4488	$224.45	$224.45	$224.40
Purchase #3	$190.91	13.168%	$216.049	$216.05	$216.05	$216.00
Purchase #4	$117.61	5.298%	$123.841	$123.84	$123.85	$123.80
Purchase #5	$59.60	10.535%	$65.8789	$65.88	$65.90	$65.90
Purchase #6	$247.82	10.348%	$273.4644	$273.46	$273.45	$273.50
Purchase #7	$87.55	9.841%	$96.1658	$96.17	$96.15	$96.20
7 purchase totals =	$1,155.96		$1,278.9299	$1,278.93	$1,278.95	$1,278.90