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	$171.80	9.706%	$188.4749	$188.47	$188.45	$188.50
Purchase #2	$91.34	8.455%	$99.0628	$99.06	$99.05	$99.10
Purchase #3	$43.59	7.496%	$46.8575	$46.86	$46.85	$46.90
Purchase #4	$10.34	10.392%	$11.4145	$11.41	$11.40	$11.40
Purchase #5	$6.73	7.128%	$7.2097	$7.21	$7.20	$7.20
Purchase #6	$249.69	7.462%	$268.3219	$268.32	$268.30	$268.30
Purchase #7	$192.54	12.753%	$217.0946	$217.09	$217.10	$217.10
7 purchase totals =	$766.03		$838.4359	$838.42	$838.35	$838.50