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	$179.86	6.644%	$191.8099	$191.81	$191.80	$191.80
Purchase #2	$85.59	12.854%	$96.5917	$96.59	$96.60	$96.60
Purchase #3	$190.53	8.869%	$207.4281	$207.43	$207.45	$207.40
Purchase #4	$40.66	11.834%	$45.4717	$45.47	$45.45	$45.50
Purchase #5	$87.59	8.227%	$94.796	$94.80	$94.80	$94.80
Purchase #6	$63.63	5.839%	$67.3454	$67.35	$67.35	$67.30
Purchase #7	$227.69	9.109%	$248.4303	$248.43	$248.45	$248.40
7 purchase totals =	$875.55		$951.8731	$951.88	$951.90	$951.80