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	$139.83	5.723%	$147.8325	$147.83	$147.85	$147.80
Purchase #2	$32.43	7.399%	$34.8295	$34.83	$34.85	$34.80
Purchase #3	$103.40	3.365%	$106.8794	$106.88	$106.90	$106.90
Purchase #4	$38.26	6.874%	$40.89	$40.89	$40.90	$40.90
Purchase #5	$241.52	13.377%	$273.8281	$273.83	$273.85	$273.80
Purchase #6	$24.60	9.414%	$26.9158	$26.92	$26.90	$26.90
Purchase #7	$28.55	13.349%	$32.3611	$32.36	$32.35	$32.40
7 purchase totals =	$608.59		$663.5364	$663.54	$663.60	$663.50