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	$248.32	12.544%	$279.4693	$279.47	$279.45	$279.50
Purchase #2	$240.40	8.726%	$261.3773	$261.38	$261.40	$261.40
Purchase #3	$182.38	4.450%	$190.4959	$190.50	$190.50	$190.50
Purchase #4	$60.66	11.331%	$67.5334	$67.53	$67.55	$67.50
Purchase #5	$242.61	9.282%	$265.1291	$265.13	$265.15	$265.10
Purchase #6	$248.29	10.168%	$273.5361	$273.54	$273.55	$273.50
Purchase #7	$111.96	11.667%	$125.0224	$125.02	$125.00	$125.00
7 purchase totals =	$1,334.62		$1,462.5635	$1,462.57	$1,462.60	$1,462.50