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	$71.98	11.219%	$80.0554	$80.06	$80.05	$80.10
Purchase #2	$229.38	9.390%	$250.9188	$250.92	$250.90	$250.90
Purchase #3	$111.83	3.170%	$115.375	$115.38	$115.40	$115.40
Purchase #4	$90.99	9.131%	$99.2983	$99.30	$99.30	$99.30
Purchase #5	$33.71	10.622%	$37.2907	$37.29	$37.30	$37.30
Purchase #6	$99.41	4.206%	$103.5912	$103.59	$103.60	$103.60
Purchase #7	$209.86	10.492%	$231.8785	$231.88	$231.90	$231.90
7 purchase totals =	$847.16		$918.4079	$918.42	$918.45	$918.50