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	$135.41	9.240%	$147.9219	$147.92	$147.90	$147.90
Purchase #2	$99.59	13.762%	$113.2956	$113.30	$113.30	$113.30
Purchase #3	$59.54	9.379%	$65.1243	$65.12	$65.10	$65.10
Purchase #4	$43.86	6.458%	$46.6925	$46.69	$46.70	$46.70
Purchase #5	$112.42	4.837%	$117.8578	$117.86	$117.85	$117.90
Purchase #6	$48.42	11.177%	$53.8319	$53.83	$53.85	$53.80
Purchase #7	$40.30	4.744%	$42.2118	$42.21	$42.20	$42.20
7 purchase totals =	$539.54		$586.9358	$586.93	$586.90	$586.90