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	$249.85	8.779%	$271.7843	$271.78	$271.80	$271.80
Purchase #2	$72.96	11.753%	$81.535	$81.54	$81.55	$81.50
Purchase #3	$105.31	10.550%	$116.4202	$116.42	$116.40	$116.40
Purchase #4	$249.86	4.790%	$261.8283	$261.83	$261.85	$261.80
Purchase #5	$77.69	9.499%	$85.0698	$85.07	$85.05	$85.10
Purchase #6	$127.70	10.763%	$141.4444	$141.44	$141.45	$141.40
Purchase #7	$69.91	13.468%	$79.3255	$79.33	$79.35	$79.30
7 purchase totals =	$953.28		$1,037.4075	$1,037.41	$1,037.45	$1,037.30