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	$38.28	8.466%	$41.5208	$41.52	$41.50	$41.50
Purchase #2	$183.85	4.342%	$191.8328	$191.83	$191.85	$191.80
Purchase #3	$79.85	5.267%	$84.0557	$84.06	$84.05	$84.10
Purchase #4	$118.68	12.166%	$133.1186	$133.12	$133.10	$133.10
Purchase #5	$38.56	12.517%	$43.3866	$43.39	$43.40	$43.40
Purchase #6	$91.87	12.460%	$103.317	$103.32	$103.30	$103.30
Purchase #7	$84.58	5.394%	$89.1422	$89.14	$89.15	$89.10
7 purchase totals =	$635.67		$686.3737	$686.38	$686.35	$686.30